I would not trust either number, but 400 seems to be closer to reality. If I burnt all the calories FS tells me I burn I would have lost myself completely many years ago. I use stationary bike daily and mine shows less than 300 cal per hour of rather intense exercise. Never was able to reach "moderate" speed of 13 miles per hour and keep going at this speed for an hour.
The first thing you lose on a diet is your sense of humor. ~ Author Unknown
It doesn’t matter what diet you follow… What matters is what makes you follow your diet. ~ Tom Venuto