Technically, if I'm correct, most sororities/fraternities are not allowed to discriminate against gender when it comes to members; however, I've never heard of a woman in a fraternity or man in a sorority so you're probably right that he didn't belong to the organization.
Like the others said, just keep to yourself. It's not your issue to deal with if someone is breaking another GLOs rules, and there could have been circumstances to it.
