You really have no idea what their intention was. Maybe their laughing was malicious, but not necessarily. It was a stack of books written by old white men. They might have a lot of reasons to find that funny without thinking anything bad about OP.

Personally even at that age I blamed culture and our education system for acting like male authors are the default for everyone and female authors are a special interest sub category. I still do, especially for teenagers who haven't had a lot of opportunity to examine their own biases.

This was one such opportunity though.

I don't see anything wrong with them pointing out the evident lack of diversity in his book selection that day.