Unusual things like mushrooms are not the same - they have a distinctive texture, which can be most unpleasant if you don't like it. DD1 used to leave a ring of mushrooms round the edge of her plate whenever I included them in anything (Now, of course, she loves them and will eat up anyone else's helping for them)
But if he makes a habit of choosing things himself and then not eating them, then he is repeatedly wasting food, and thence money. If what is on his plate is what he put there, then it can be reasonably assumed that he likes it and wants it, and he can learn to gauge just how hungry he is and choose accordingly.
If everyone did the same, there would be less food bought just to throw away - and perhaps it would extend into buying things for the sake of spending money. There is a lot of obscene consumerism to contrast with real poverty and deprivation.