Yes, in the pizza example Emw showed, the definition of "food" is important. If what I ate this morning is a food, then pizza is a subclass of food. This is consistent with the first sentence of
https://fr.wikipedia.org/wiki/Nourriture of frwiki. And the fact that "pizza" is an instance of food is a mistake, unfortunately a pretty common one on Wikidata. We should write a query to find all such examples where an item is both an instance and a subclass of the same class.
Now pizza is clearly a type of meal it could be relevant in a food classification and could be very well be an instance of it, as it's a preparation common people used to put whatever they can put on it, similarly to