I really do think he was just absolutely out of it, potentially blacked out and went over, either that or perhaps trying to climb onto whatever was beside his balcony, knowing they didn't want him to leave his room. The boy was absolutely out of it, going by the pictures of the room. But I wasn't there, and that is only my opinion.
Honestly, the amount of people who think they are invincible on drink or drugs is mental, one season alone in Magaluf I think about 6 people had fallen to their deaths although not all solely down to drink/drugs - one girl had got locked out and was trying to get onto the next balcony to get into her friends apartment
I don't think we will ever find out the truth sadly, we can all only speculate. Either way, its a sad end to a young life.