Taste, texture, appearance?
I'm pretty sure that I could distinguish the body of one from the other. A man's ham would be considerably smaller than that of a full grown swine.
I've read that those that have eaten both say that man tastes like monkey.
But if man tastes like pork, it probably explains the popularity of cannibalism throughout prehistory. well, that and the struggle to obtain enough calories.
If seen as entire chunks, the anatomy might be a giveaway, but cut into servings, probably not. Pork was very popular in Roman times, but would be expensive; otoh, when the “games” were going, the supply of, shall we say, good substitutes was plentiful and cheap. It wasn’t a good idea to order pork at those times, particularly near the arena.