Yes, the first one matches only 2 more characters while the second matches 1 or more. Also the +? is a lazy quantifier so it will consume as little as possible.

I also don’t see how the term applies only to ActivityPub, wouldn’t any federated protocol ecosystem be a ‘federated universe’?

Matrix is federated though, so why wouldn’t it have something to do with the fediverse? Is that not the definition of the term?