Well, more specifically, he confirmed ties to Tam-Tara Hard. I know it's probably not much of a distinction, but consider the following:

-While they said veteran players who have clear Tam-Tara Hard will get more out of the PotD story, it still aims to be comprehensible to those who haven't gotten that far. While it's true that Edda's story gets its start before lv17, she shows up as a fairly stable and sane Conjuror around that point as well. Now, the story could just have her appear deeper in the dungeon and have the player fill in the blanks, but...
-They're still playing coy with the identity of the girl, and her clothing doesn't match anything Edda has ever appeared in - not in the early MSQ, not in Tam-Tara Hard, and not as a rare apparition around the City-States.
-The Avere-esque Voidsent is significantly smaller than what we faced in Tam-Tara Hard.

While I can't say any of that makes me 100% certain it's NOT Edda, I don't think it's as much a confirmation as people are making it out to be. Alternate theory? The connection is more to the necromantic lore that figures into Tam-Tara Hard than to Edda and Avere specifically, and our mysterious figure is some Voidsent or otherwise necromantically-inclined void-mage who has dabbled in similar things (and maybe even had a part in Edda's education in that area).