Nature of the Sound

[Kesey]

We have no evidence Hythlodaeus was correct. So far as we're aware he had no direct connection to the Anyder, so his statement may simply be what he (or Emet) believed.

Hythlodaeus corroborates the evidence found in the Anyder, pertaining specifically to the summoning of Hydaelyn. I find it hard to contradict a direct recording of the Ancients (Anyder) which follows in the wake of a self-aware reproduction of Hythlodaeus that speaks with the knowledge of having seen all the events (lets also not forget that he's on Emet's side!).