I would suggest that you read Jonathan Haidt's book "Why Good People are Divided by Politics and Religion". He delves into the ways that different ideologies approach life. Also Kim Holmes wrote "The Closing of the Liberal Mind" which is a fascinating read for anyone who has had to deal with a so-called open minded Liberal. These books will answer your questions!

I believe this is a limiting statement. You will find both closed minded and open minded in the liberal camp and the conservative camp. This is the same with any label that can be placed on groups. Most large groups are far too diverse to accurately apply such a label.

The key to positive change is to openly and respectfully listening to all points of view. Additionally, it is key to understand that just because another individual disagrees with you, does not mean they are closed minded, it just means they have a different point of view. Lack of agreement does not equal closed minded.

I think one phenomenon we are dealing with is the flattening of the distribution curve. So when we traditionally think about conservatives they were the establishment who saw change a slow planned evolutionary process. Where institutions were enablers of change. Where as liberals saw the institution as preventing change and were more idealistic about the value of ideas and how they good revolutionize the human experience. With the glttening of the curve the person one std devotion to the left now has a greater degree of difference to someone one std deviation to the right. Therefore they find it harder to accept the alternative point of view. However what is really happening from a societal point of view that we are all feeling is that there are more people at the extremes of left and right and their behaviors are so uncharacteristic that they confuse the definitions. To my my a left extremist is exactly the same as a right extremist. No tolerance for any other point of view, totally dissatisfied with how society functions and wants it remade in their image, are only interested in power to achieve this regardless of the cost, the ends always justifies the means. Modern communication systems have unfortunately given them a voice out of perspective with their representation in the population.

Here's the main point from my perspective. People on the political right value empiricism and look at reality. Leftists are more idealists and value emotional fulfillment. So it's more a dichotomy of mind vs. emotion rather than open/closed- mindedness.

Willingness to try new things and seek new experiences is a liberal perspective. Do not misconstrue the progressive movement which while leftist is utterly illiberal. Today you are more likely to find an open minded fiscal conservative than you would in finding a college professor. The political right in the US is on the outside looking in, they are reviled in the media, and on the college campuses. The right is associated with the 'rubes' in country side. The old-guard/leadership in the GOP, which is progressive, hates their own voters. This is a recipe for being willing to listen to anyone who is not despising you.

I think if you take an honest look on both sides of the isle, you will see equal numbers of closed minded and open minded individuals on each side. However, the close minded on both sides of the isle seem to be the loudest, drowning out the majority.

What I love about this site is that people from both sides can have an honest, open, respectful dialog.

A Liberal is so 'Open Minded' that they refuse to listen to anyone that disagrees with them, will riot when a Conservative tries to speak at a Campus, will attack those that have a Trump Hate. ........... I could go on and on, but a Liberal is sooooooooooooo closed minded that their lives are ruled by their anger and hate.

Just found this related article: Why Liberals Aren’t as Tolerant as They Think
The political left might consider itself more open-minded than the right. But research shows that liberals are just as prejudiced against conservatives as conservatives are against liberals. (By Matthew Hutson May 09, 2017) [politico.com]

The question is hard give a black and white answer as you might have noticed with the previous comments. I would like add 'perspective' as another factor. As a Dutch immigrant, I grew up with conservative values. Immigrating to Texas I found out that I am extremely open-minded compared to the average Texan. Being open-minded is a matter of perspective towards the community you compare yourself to. Does that make me less conservative in Texas? No, I think the political climate made me even more passionate than before.

Personality psychologists all agree that when it comes conservative and liberal political orientations, Personality traits openness experience and conscientiousness are closely related political orientation.
High scores in Openness and low scores in conscientiousness are more liberal. High scores in conscientiousness and lower scores in openness are more conservative.
Conscientiousness is broken down the facets industriousness and orderliness. Orderly people like borders and that makes them more conservative due order and tradition. Openness can be broken down the facets intellect and aesthetic appreciation. They like open exchange of ideas, therefore, more liberal.
And we need both for a and functional society. Too much order and the structure ossified into totalitarian dictatorships. Too much chaos and new ideas lead to authoritarianism as synonymous with compassion.

I'd say it's strictly a personality trait.

I think Peterson is referring more to personality than directly to political theory. By 'liberal' he means, 'eagerly embracing new ideas' and by 'conservative' he means 'holding onto old ideas'.
These often spill over into poltics. But nowadays it is kind of radical thing to go back to very old ideas as if they were fresh things... thus you have a lot of 'liberal' people on the 'conservative' side of things.

The first question you need to clarify is whether you are asking about “Classic Liberalism” (prior to WWI) or “New Liberalism” (since WWI)
For instance, I consider myself a Liberal Constitutional Conservative based on my understanding of Liberalism ... where Liberalism is very closely aligned with conservative thought processes.
Perhaps you should look into the concept of which Liberalism you are asking about as the current version of “Liberalism” is a Leftist Distortion of the term.

You might consider checking out this free ebook written in 1927 by Von Mises: [fee.org]

"If you're not Liberal by the time you're 20, you're heartless. If you're not Conservative by the time you're 40, you're brainless." - Winston Churchill

I’m not sure that it’s a matter of closed mindedness and open mindedness. Perhaps more like creative versus process driven. How open minded can the left be when they are shutting down speech at universities, attacking people wearing Trump hats and silencing virtually any opposing thought? Finally, I love that Peterson says that we need both types of people in society.