At least he isn't shocked to see his face, which means it's definitely not the same sort of memory issues he had when he'd returned before. So what was it? If even his soul-twin couldn't recall why he was here, maybe he'd stumbled onto something he shouldn't have? What other reason would there be?

"It wasn't me!" he's quick to insist, "you were out here shambling around like an old corpse. I was about to ask you the same thing."