Quote Originally Posted by Veloran View Post
Seems to me the answer is that he put them there beforehand.


Hythlodaeus is just Emet-Selch's construct. Anything you attribute to him is in reality Emet's will by proxy.
Hythlodaeus himself observed in the DMV scene how he had more autonomy than the other reconstructed ancients.

That said given Emet's spirit appeared in the Elidibus fight I am inclined to think he was the one who set the crystals there. Plus how would Hythlodaeus have even gotten them?