There's not much middle ground between "try to have some fun at work because there's no reason not to" and "don't do something someone might take issue with". A completely sterile work environment isn't really any better, and for some it's definitely oppressive and worse.

Is it sometimes an intentional cult-building tactic? Definitely. Is it always? Heck no, people come up with in-group names all the time. Groups of all kinds develop their own terms and memes and whatnot, it's normal.