Except that Sa'ara didn't do it because nowhere does this Naaru mention this situation explicitly. It was simply Calia's own interpretation, motivated by that Forsaken who came up to her and told her he's down. That's all there is to it. While it all might allign and in truth be some super evil Naaru plan, it was certainly up to Calia's character to see what she wants to see.
Blizzard's way of writing the Naaru into being these tyrannical Light-based leaders is comical because it is obvious how they are forcing this narrative into everything now in order to counterbalance a decade of lore that went the other way.