I'm pretty sure Thordan's English translation says "what are you" simply for for dramatic effect. It isn't consistent throughout other languages (as with other parts of FFXIV). I've seen where others have stated that the translation is more akin to "Just what kind of human are you?" and similar sentiments.

Personally I don't think there's any good reason to suspect that the Warrior of Light is a primal. The Warriors of Darkness showed us that other worlds also have their own champions, and they are not Primals either. They are just people trying to save their existence.