Unfortunately this is one of the issues with federation. In the future we would like to have all the identity based communities either beehaw users only or locked down from comments/posting. We have no control over other instances, but to remove their content or remind them how to act here. I've personally been avoiding a scorched earth policy for non-beehaw accounts, but I'm slowly finding myself leaning towards it because of behavior like this. I've cleaned up some of the worst of it, and I'm keeping a close eye on a few folks in this post.