Sending as a second comment cuz I just now read your source, but it's different than what my original comment was.

I didn't realize the density that GPL code puts into your project, it does seem upon looking into it that that is correct that he cannot under GPL terms redistribute that software under the license that he's chosen. He is violating the GPL by doing so, because even with permission of the contributors, GPL code cannot be converted over to a lesser freedom code without a full rewrite, because code that was generated while under the GPL can't be locked down at a future date via a license that that is stricter than the existing one. The only thing you can do is make it less restrictive than GPL.

That being said, the only people who can report violations of code that is not following the GPL, are going to be copyright holders so if everyone was indeed okay with it there's no one who would be able to pursue the violation anyway