Honestly, this is disappointing, but not particularly surprising. It's a problem that's at least as old as Usenet, in terms of different communities not getting along. It's also not uncommon that people setting up instances are new, inexperienced with moderation, and sometimes even just let people register without any kind of verification because why not?
I think an important point is for admins / mods from various instances to try to get on the same page, in terms of policies. Building that common ground early, and establishing best practices, really helps mitigate a lot of the BS that can happen.