Why Birds Survived, and Dinosaurs Went Extinct, After an Asteroid Hit Earth

Sort of implicit in the article seems to be small body size too. Before the extinction event, there were a lot of ceratopsids which were beaked, but also quite large. It's not great to have a big body when you're trying to survive for years in a climate where little actual food exists.

Anyway, my problem with the argument is that some mammals obviously survived. Why? We had worse lungs, roughly the same amount of protection against the cold as many small dinosaurs... so what gives?