Not sure. I’d guess they do if they’re in a country that has IP treaty with the US but that’s definitely a lawyer question.
Even hosting your own instance that copies down the content and only federates out your comments or non copyrighted material can be tricky depending on how the fediverse works (where’s an uploaded image kept when it federated out to a server?).
Is there a copy or just a reference to the original instance?
I’d be really interested in knowing how that works