there's an unrecognized genius out there that realized you can just apply a bit flip to get that out there. That John Carmack hasn't claimed it as his invention when he could have, speaks volumes about his character.
Except he couldn't have even if he wanted to. There's always the risk some former 3dfx or SGI graybeard comes out with some paper binder with the original implementation, and calls you out on your bullshit if you do. When you're such a famous public figure no way you ever risk lying in public. Even if he were to getaway with it there was nothing for him to gain: he already has all the fame and money from honest work, there's no point risking it all to claim some piece of code.