Why did i lose weight when i switched from beer to rum?

i'm a semi alcoholic, i only drink on my days off but when i do drink i go all out and get hammered to the point of unconsciousness! i used to drink four 32oz bud ice beer but switched to bacardi rum, 35% alcohol with coke, i haven't switched my exercise regiment or my diet at all! how the hell did i lose 15 lbs in 1 month? i never weigh myself but i saw my cloths fittin a little tighter and feelin a little lighter? how did i lose weight?