There are at least parts of their tales at are true, yes. Some time ago, human mages found a way to enter the Fade, the realm of the spirits, physically. At its center is a city, blackened. As the Chantry tells it, the city was once golden and served as the seat of the Maker, and that these mages who entered His realm sullied it, turning it black.

[He makes a flippant gesture.]

One of their own claimed the city was already blackened when they found it. He was also insane and sought god-hood for himself, so who's to say where truth ends and legend begins?