A lot of this info, or info like it, came out years ago when Oher originally made his discontentment with the movie known. That's why I said this case is bologna. Oher is getting used by sketchy lawyers. This all stems from him thinking he should have gotten more money from the movie than he did, and thinking, wrongly, that the family got a huge payout from the movie and kept it from him. He is just wrong and lawyers are happy to profit off of it.
I'm sure it was all explained to him at the time he signed it, but he likely did not fully understand, because it was all over his head and he is not the sharpest tool in the shed.