On the other hand, their wiki is hosted on "The Common Lisp Wiki", all the libraries they mention are exclusively Common Lisp, and their mailing list descriptio

On the other hand, their wiki is hosted on "The Common Lisp Wiki", all the libraries they mention are exclusively Common Lisp, and their mailing list description says "The purpose of this list is to provide community to Common Lisp game developers." But it's irrelevant in the grand scheme of things... The purpose of the thing is to motivate yourself to make a game; there are no winners or prizes or anything. So if you like, you can put your name on the list, and if your finished game is "disqualified" for being in the wrong language, you've still got your game, so you still win.