Any negotiations were completed ages back when the original contracts were signed. He's simply trying to enforce their obligations and collect his entitlements

Any negotiations were completed ages back when the original contracts were signed. He's simply trying to enforce their obligations and collect his entitlements. There's no reason to sign an NDA and constrain your rights just to do this. Let's be clear: The NDA is PR-motivated insulation to dissuade him from doing exactly what he's doing now. I wouldn't sign it either.