This is why I liked college way more than HS. You could bring in a full ass burger combo and chow down during a lecture and nobody gave any shits. As long as you didn't make much noise and the food wasn't too fragrant.
But teachers like this in any level of education can fuck right off. People have shit going on and you don't know their story. Maybe they're diabetic and need something to bring their blood glucose up, or they have some kind of anxiety or other disorder that snacking can help with... As long as they're not disturbing the rest of the class, leave it alone.