There were supposed to only be six people who had ventured into the Nightmare of the Tomb of Ariel, after all. And since none of them was the author of the report… then who the hell was? And how did that person know so much about the Great River?
I think it was luster who's still stuck in his first nightmare, and if he's alive he's in the desert longer than any of them , maybe he's stuck there ? wild hypothesis but it'd be a really good twist