It appears to be specific to replies to replies - this video on peertube.wtf has a top-level comment from PieFed.
PeerTube's federation model is different from Lemmy's - they don't sign remote comments when they federate them out again, so it's often up to other instances to fetch them from the source. It might be that PieFed has to do something to help the likes of peertube.wtf successfully retrieve a comment when it's a reply to another reply.