You mentioned that people do this all the time. Why didn't he say something similar about whatever other demographics asked as I imagine that it's not only females who do so.
Also, I feel I should point this out. It's asking him to put a book back. My friends and I do similar things for each other all the time, and don't feel the need to state that we're not independent, equal individuals. The sexism in his behaviour arises from his singling out of one demographic based on one person who asked him something that is far from uncommon, and in the fact that he didn't think "Man, if blondes/brunettes/students/nerds/young people want equality they should do things for them selves," it was women.