Ron was still wandering alone. Yes he knew this was a bad idea, yes he had better things to do- but Aberforth had pulled him aside the other night and told him he was being cut off from the barstool - and Rosmerta at the Three broomsticks agreed.
Apparently running into a 'poor bloke' and trying to beat the shit out of him implied that he had 'an issue with self control'. So, since he couldn't drink, and couldn't sleep - the next best thing was to walk himself into exhaustion. He had already wandered as close to the forrest as he dared do by himself (he was foolish, not dumb) the night before, Ron had decided instead to wander up towards the lake.
At first he thought the splashes was the giant squid entertaining itself in the frigid water and had ignored it. It wasn't until he came upon the shoes at the edge that he had any concern. "Hey!" He shouted out into the black. "You okay? You - what the hell mate???"