To be fair, they did specify right-wing Lemmy instances, not right-wingers in general, and I can't think of any instances that would meet that definition off the top of my head.

But Hexbear definitely has a reputation as some of the worst of the worst of the normal instances. Blahaj defederated from them despite Ada trying to get the trans communities of both instances connected because of the harassment, brigading, and outright transphobia Hexbear inflicted on Blahaj users for not being the right kind of leftists. You can still find the community discussions on the topic in the general instance posts. They even tried to claim that Blahaj was being transphobic to them. You know, the LGBTQ instance created and ran to be a space for trans people and others first and foremost.

Hexbear is also known to have at least once tried to convince their mods to "take over other instances and ban all the non-communists."

I believe that at this point if you were to download the stuff to spin up your own instance, Hexbear is on the list of instances that are defederated by default because so many instances have defederated them because of their behavior.