Anyone can lose weight, anyone can get fit.
The things that stop us have nothing to do with what diet we are on, what exercise programme we use. It's what motivates us, how much we want the end result, how driven we are to achieve that goal and how important it is to us. Also, how much we enjoy what we are doing.
He will still have an amount of muscle underneath all that fat. I doubt that he is eating excessively over what he used to eat, just not exercising and therefore burning the calories. He can't replicate going from couch potato to fit, he didn't start as a couch potato and his calorie burn will probably be greater.