You don't understand.
Although a pound of fat contains something like 3500 calories, it doesn't work to calculate in reverse. The body burns more than just fat for energy.
Also, you aren't taking into account what your body burns at rest, which is called your resting metabolic rate. Most people burn an average of around 1500 or so calories a day just being alive--but it varies depending on your age and current weight, etc.
It's not so simple as you ate X and burned Y with exercise. Your calorie deficit is how much you ate, minus your resting metabolic rate, minus your calories burned with exercise.
But don't take those numbers too seriously. Calories burned is often just an estimate, rather than a precise or individual measurement.