Are your confusing nutritional calories with physics calories? When people talk about diet, of course they are talking about calories obtained from digestion, not combustion engines.
Energy is energy, a calorie is a calorie in gasoline, food or electricity. However when talking about nutrition labels, those are generally an estimate of calories potentially extracted by humans (which I think is what you mean with nutritional calories). I'm not confusing anything. But some people seem convinced that the car analogy is exactly how the human body works - you put food into your mouth and it gets "burned" by exercise or stored (calories in, calories out) and no amount of evidence or science seems to convince them otherwise.