Are you saying that a problematic thyroid gland can cause you to metabolize fat from air?
Because, y'know, the dear old (calories in - calories out) equation is at least consistent with things like thermodynamics and conservation of energy.
Oh look, you did GCSE physics and think you understand biology. And I suppose if you hang by your arms this doesn't count as exercise because you're not moving?
You never considered that if you eat 1000 calories and only require 500, your body might not use the excess but dump them, whereas his body might hold onto every calorie regardless of requirement?
Your weight gain is strictly governed by calories in - calories out, but neither of those values is what you think it is.