I do think some areas have more interaction between students at different colleges than others, and I think a lot of that can just be a product of practical proximity. If the colleges in question are close enough to easily get between, share local clusters of bars and restaurants, share off campus housing neighborhoods, and so on, it is natural there would be more spontaneous or easily-arranged interaction.
I’m certainly no expert, but my sense is that it is true that Boston college students often experience a lot of that. I happen to know they do in Pittsburgh as well–Pitt and CMU are right next to each other (and actually, you can take classes at either), and then there are more colleges in the same part of the city (known as the East End). And then students from the East End colleges are often living in the same neighborhoods, going to the same bars and restaurants, and so on.
So I do think this is a thing for a prospective college students to consider, if that is there sort of scene at least.