non-free, non-libre and proprietary are synonymous, and even closed-source is essentially synonymous, except for the different alignment it conveys. I'd say a game that contains any nonfree component, be it code or artwork, is nonfree as a whole, because a freedom-respecting component means it doesn't take freedom away, while a freedom-denying component means it takes freedom away, so the combination thereof takes freedom away. but that doesn't prevent components from being freedom-respecting.