I don't think the person put in the cluse by himself, surely AMD would have known and agreed to it. They would own the output of any of his work anyways, it was only with their approval was he was allowed to take ownership or release it. I do think this is splitting hairs, AMD isn't the savor here but I wouldn't say they don't get any credit either.
"They" (being AMD) didn't. The person they contracted put in a clause that allowed him to open source the work (years AFTER) AMD stopped paying him.