Now you could try to argue that it's copyright infringement but there are many solid arguments as to why these model weights don't meet the threshold of copyrightability.
You could also try to argue distribution of trade secrets, but facebook doesn't seem to view them as such - shared with little restrictions to anyone with an accedemic email, no vetting or ndas, etc.
I personally think that facebook planned all of this (sans the childish behavior occurring on their github repo, maybe). They probably wanted to release a capable language model publicly but didn't want the legal and social liabilities associated with it.
Facebook is no stranger to keeping things secret. I simply refuse to believe that they didn't see this happening.
(Thank you, Facebook!)