Could it have been YEAST? Mushrooms are fungi, and yeast is well... yeast, but they have a relation in the "crap that grows all by itself".
It may also have been a whole milk cheese vs part-skim that most places use.
I'd bet you though if you called that place, spoke to the owner, and asked, you might get an answer. If there's anything we like, it's talking about our masterpieces.