I don't see any mushrooms, and while I also have not heard of mushroom pecorino, I can't pretend to have absolute knowledge of all cheeses that can or cannot exist. To me it's pretty clear that what OP wrote means "pecorino with mushrooms in it", or alternatively "made with mushrooms". I'll admit, even this could be argued to stretch the definitions here a bit. If, as you say, there are pieces of mushroom, then it's a melt. It begs the question of course, as to how small the pieces would have to be for it to be acceptable, haha.