Calories in food and calories as measured in physics are not the same. Nutritional calories exclude non-digestible components, excluding dietary fiber and artificial sweeteners; both of which could be burned in a bomb calorimeter to generate heat.
Many of these human non-digestible components, like cellulose, are the primary energy source for other specie
Human calories are dependent upon the body’s ability to catabolize them, usually involving enzymatic action; rather than a high-temperature oxidation reaction.