PeerTube work just like Lemmy, when it comes to federation. If you are on the front page of Lemmy.wtf you only see content that is federated specifically with lemmy.wtf. On PeerTube.wtf you also only see content that is federated. However, PeerTube support a “global search” that uses SepiaSearch and SepiaSearch knows about pretty much every PeerTube instance. So when you use the search box on peertube.wtf, it will search beyond the instances that federates with peertube.wtf.