LOL well yea considering how much motion capture is out there just under CC0 alone. I have some True Bones packages and there are more than a few takes in the package that is questionable as to it’s origin.
Carnegie-Mellon Graphics Lab Motion Capture Database for example has been out for years under CC0 and has been converted to and included as part of a lot of different animation packages for sale or other wise.
Now he may or may not have a case but just because of the nature of fair use assets there is no way of really knowing 100% the origin of the asset in hand and if the animations used was bought under fair use licensing there is no reason that this should have been an issue in the first place.
Sorry to get snippy but when a asset provider starts making ownership claims it ticks me off as once purchased under fair use it’s none of their business as to how it is used after the fact.