Gatekeeping really is not either of these things, but people can wear whatever they like. I can't say I get why someone would do it at all, but not my problem.

There's a huge difference between using it as a conversation starter and asking about their favorite songs or whatever, since it's reasonable to assume they know and like the band, and going "name 3 songs" because you assume they don't listen to the band and also somehow care about that.