The restaurant industry certainly is not a market resembling perfect competition, I mean we can just look at the vastly varying prices between restaurants, which certainly can't be attributed to cost. Even if we talk about the food industry more generally, I mean there's like 3 or 4 different brands of milk in my supermarket which vary in price by 100% I hardly doubt that their cost varies by that much.
https://en.wikipedia.org/wiki/Perfect_competition