Notably, while Francis is sometimes considered liberal, there weren't (m)any notable changes to Church doctrine during his papacy.

He did have a habit (a good one, IMO) of speaking more off-the-cuff in interviews. Whether that was contrived, or just a natural part of his personality, I do not know. But, it was those comments that usually led to the "he's a liberal!" comments. And both sides of the political spectrum said similar things... "He's a liberal (like us)!" or "He's a liberal (unlike us)!" - so he was probably doing something right.