If he had worded it differently and been less aggressive, people would have been more receptive. "A calorie is a unit of heat energy" which means anything that burns has calories. But obviously people can't drink gasoline and eat charcoal to survive. Calories are measured by literally burning the item and measuring how much heat is released. Some foods will have lots of calories and others can't really be burned without adding something extra. People get calories from breaking down a food source, but some foods are way harder to break down via their digestion compared to burning, while some foods can't burn but are easily broken apart inside the body.
Take grass for example, some animals have to eat that shitty grass all day long to get barely enough to scrape by. If I collected a large amount of dry grass and burned it you would see a nice flame, clearly grass has tons of calories right? But it doesn't, even the most efficient grass eaters in the world will be forced to eat their own shit in order to not die. So if I gathered up a ton of wheat and a ton of regular grass and burned both of them they would have the same calories, but a loaf of bread can have 2000 calories.
Basically what I'm trying to say is calorie counts can be REALLY deceptive. There are so many variables involved in getting energy from what you eat, whats true for one person won't be true for another.