It is one of those things that I always thought was implied. I can't think of too many things that are "sentient"/"demihuman" type races that are specifically mentioned as eating human flesh. It seems most things that do are dehumanized/more primal/mindless. I am speaking broadly because I've yet to find any fantasy novel/movie/game/etc that is dark/gritty enough to have that as a specified act (aside from Game of Thrones, but no mention of goblins so far).