They're not singling out the nerd, they're talking about someone's idiosyncrasy. Tomorrow, proverbially, they could be talking about one of Gillian's idiosyncrasies. I don't think it's immature or callous. It's just a group of people reasoning about something.
Maybe I'm wrong but the whole thing felt very weird to me. Can't put my finger on it.. I want to say immature, but it's probably just unempathetic. I think my brain reached out for "immature" because I saw a lot of it among the "popular" kids at school.