So with Argus coming and the Draenei history about to be revealed in a Chronicle at some point I figured it would be fun to put together what lore we do know or can infer from the game.
Basically I want to talk about the Draenei and the light, so this is all going to be inferred.
The Draenic civilization on Argus was one purely of the intellect and the arcane. While the light was unknown or close to unknown the lust for power was not - which led to the rise of the Manari. The Manari were warlocks, pure and simple and ran the risks all warlocks do of losing control of their demonic slaves, which is how we have the Skull of the Manari as an artifact weapon. I'm not sure if Thal ran afoul of the Doomguards prior to the creation of the Legion or only after the corruption of Sargeras but either way there wasn't much control placed on the thirst for knowledge on Argus.
So I theorize that while Velen may have made contact with the Naaru either right before or right after the corruption of the Draenei I'd say that it was only on their exodus that the Draenei became true scions of The Light while under the tutelage of the Naaru.
This reflects pretty boldly on Azeroth though, as Azeroth came by the ways of the light in a rather natural way and thus may have a stronger affinity for it, which is why Azeroth is needed to truly defeat the Legion as part of the Army of the Light.