'Food' does NOT need an article in this answer. "Food was cooked." focuses on the fact that some kind of edible material was cooked. "THE food was cooked." indicates that the particular food that was ready to be prepared is now cooked. However MEAL was cooked DOES need an article. If it does not have an article, it is assumed to mean 'meal' in the sense of course flour, e.g. corn meal.

The designers really need to make up their minds about when to require "the" and when to mark "the" as wrong.