Food is a non-toxic, organic substance that provides nutrition in the form of carbohydrates, protein, fibre, fats/oils, and/or vitamins and minerals. Sure there are some edge cases which you can argue the point in, such as a lump of rock salt maybe, but for the most part it is something which provides sustenance. Sure you could eat mud or plaster and it won’t kill you, but it won’t help keep you alive either, so its not food.
I agree that the pile-on wasn’t necessary, people tend to just give their kneejerk response and then move on. Having said that, you probably could have explained your case a bit better too in the original post.