I eat so much but have very little fat, why is this?

I probably have on a daily basis in the 6K calorie range and about 130g of fat. Here's the weird part- I have a little belly, but barely anything at all. Just enough that it moves a little bit when I jump, not even when I walk or run. But why am I not the size of my car? I am a 30+ mile a day biker, but I don't think it's enough to burn all that off. I've been eating like this for years, but I've never been close to overweight. I weigh 245, but according to my doctor overweight starts at about 280 for me since I have a seriously huge frame and 18" arms of solid, hardearned muscle.