This is what naive calculations say, this is not what a DEXA scan says. His body is actively reducing calorie expendature well below what you would expect.

I have tried taking over his calorie counting for a week to help him, as someone who manages my own weight successfully I don't think I would overcount by a factor of 2. The chance he ate calories I was unaware of during that week is approximately zero (highly controlled environment, never left apartment)