Sorry to hear about your cousin.
Basic science says that to survive any warm blooded creature needs :-
Shelter / warmth
Water
Air
Food
There are no calories in shelter unless you are eating the furniture in which case you have more severe health problems to worry about that being overweight.
There are no calories in water and I do mean
water not bottles of fizzy pop.
There are no calories in air unless you work in or live down wind of somewhere that utilizes powdered sugar by the ton.
There are calories in food.
I'll take your word that he wasn't cheating so that leaves the hospital were over feeding him.
Some may be down to water retention but you can get medication to control that if the hospital had bothered.
At 70Kgs your cousin would only be obese (as this is what this thread is about) if he was under 5 ft tall.
http://www.nhs.uk/Livewell/healthy-living/Pages/height-weight-chart.aspx