Well, your body's going to use whatever calories it gets from food, too. Calories from protein aside, I don't know if it burns body fat in tandem with dietary fat, or goes after body fat only when the gut is empty.
Anyway, supposing you eat nothing all day and are in ketosis, my understanding is that you will burn fat equal to your BMR plus the calories from exercise. BUT, there will likely be a touch of catabolism, depending on how active you are. I don't think that's anything to worry about for one day of fasting.
1331 calories from 7 miles of running seems really, really high. How long did that take you? Keep in mind that that will include your BMR. Like if a treadmill says you burned 300 calories in an hour, and your BMR is 2400 (100 per hour) then you actually burned 200 calories through exercise.
You lousy kids! Get off my savannah!