That's a bit of a wild interpretation of copyright law.
I mean, Anthropic isn't going to fight it because it lets them do the thing they want to do, so I can see how this never gets beyond the court that allows them to do the thing they want to do.
But would this argument would have flown in the past?
It wasn't even attempted in Sony v Universal. Or any copyright suit up until this point. That doesn't smell funny to you?