Well, they say development will be "in the open" and that "[w]hen the game is playable, it will be free. Not free to play, just free." So they use the words "free" and "open," but they don't say anything like "free software" or "open source." Even someone like Stallman acknowledges that this is a legitimate use of the word free (although the terms "gratis" or "free as in beer" are less potentially ambiguous).