An interview with Gaider a while ago had Gaider confirm that the Architect was an ancient magister. I can already imagine the rage if he winds up returning even after getting killed. More reason to keep him alive and friendly to me.
Gaider never said that.
He said the character's arc in Awakening followed the same logic for the one used in Corypheus's story (before Inquisition was even released, so I assume he was talking about Legacy DLC).
And said arc is: the great revelation -the identity of the person behind all the mess - comes only in the end.
If Gaider intended him to be a magister, he'd have written so in The Calling.
In the book, nothing is ever stated that can lead to the conclusion that he's a magister.
This mistaken notion that he's one of the original Seven came to be because of his human like appearance in Awakening. But in the book, where he FIRST APPEARS, he's a regular, ordinary emissary.
The only fact we know about him and that hints at him not being usual at all is the fact that he's immune to the calling. But the ancient Magisters are dakspawn, so they can also hear the calling. Therefore, this doesn't help much the whole "Architect is a magister" theory...