Er I thought the whole point of the fade section
Not necessarily. You could make the argument that the Quizzie walked in on the ritual at the most crucial moment, and that s/he was guided by Andraste there. You could say that Andraste protected the Quizzie, keeping them safe instead of dying horribly in the Fade. Even if the spirit guiding you in the Fade wasn't Justinia herself, it is indicated by Cole that it was a Spirit of Aid, sent to help and protect you. Who's to say that the spirit wasn't sent by Andraste, or is even a part of Andraste herself?
Regardless of whether Andraste put the mark on the Quizzie or not, s/he should have died like 10 times over by the time you even GET to the Fade. Surviving the Fade in physical form the first time, AND the second time, AND the explosion of the Conclave, AND the attack by both Corypheus and an Archdemon (which I personally would count as two alone), AND the avalanche, AND (if you help the mages) traveling through time itself using an unstable spell that shouldn't even work, AND all the fights they get into just being themselves. If that isn't divine intervention and protection, I don't know what is.
Varric's reaction is the most telling when asked if he thinks the Quizzie is actually a Herald, blessed by Andraste. Now, keep in mind Varric isn't really religious. He's probably an Andrastian in the loosest sense of the word, but when you ask him what he thinks of being sent by Andraste, he says (albeit hesitantly) that he agrees with that. He says himself that the Inquisitor should be dead. They should not be alive at Skyhold when they speak to Varric. They should either be in the stomach of an Archdemon, trapped under 800 tons of snow, died in the Fade, or adorning Corypheus's throne as decoration. It is nothing short of a miracle that the Inquisitor lives through all that, and pretty much everyone believes it. Whether or not the Quizzie got the Anchor by accident, they have it now, and they're saving the damn world. In the eyes of any religious person, that makes them a herald of any god they like.
(Editing because I thought of more scenarios where the Quizzie should have died.)