Biology is sexist. Almost every society is like this. There are different roles and acceptable behaviors for men and women. That being said, this is not the sort of girl you want to get involved with lolJapan is very sexist, actually. If genders were reversed, people would find it super disgusting and it wouldn't be published. I think this is straight up sexual harassment. The boy will most likely think it's not a problem in the future chapters but it actually is.