I think this is a thoughtful review of the book and some of its major points:
https://greatergood.berkeley.edu/article/item/are_college_students_really_against_free_speech
And again, my memory may be hazy, but I think the authors said they focused on events at more “liberal leaning” schools because historically such colleges had been considered places where free speech and freedom of expression were more accepted and encouraged.
They also talk about how at many colleges the faculty is heavily made up of professors who consider themselves left-leaning or liberal (esp in the humanties, they have data and research on this), and that fact (that there are fewer professors who are conservative) can create an echo chamber and an environment where there is less discussion or consideration for other viewpoints because everyone already agrees with each other.