Previously, a Meta executive in charge of project management, Michael Clark, had testified that Meta allegedly modified torrenting settings "so that the smallest amount of seeding possible could occur," which seems to support authors' claims that some seeding occurred.
It really seems like their defense is coming down to "we may have seeded a little bit but there's no proof"
Not only is there the issue of getting approval from the video creators, there's the issue that most PeerTube servers aren't ready to handle a huge influx in uploads, as this would likely be a bulk operation.
Personally I think mirroring YouTube content would be more viable once ActivityPods lands and is integrated with PeerTube, which could potentially let you self host your PeerTube account data while still being part of a separate "home instance", which would greatly help with the storage issue for PeerTube as we could all bring our own storage.