It makes perfect since....the smaller you are the easier you get drink
me (6' 220) and you (5'6" 115) go to a bar......you may very well be waisted after 1 beer, while i being much larger having more blood and body mass will be barely affected after 1 beer.
The fewer beers you drink the less money you spend on drinks, therefore if he is drinking to get drink it will cost him a lot more to get drunk than yourself.