The part that puzzles me in Redcloak's Crayon recap of TDO, is that the knowledge about the goblins being created as XP Fodder is supposed to just come to him infused when he becomes a God. Yet more basic things like the existence of the Snarl or the fact that there have been a bajillion worlds before this one, do not.
So, reading that scene again, I think the information that the Goblins were created as XP Fodder was either told to TDO by another God (maybe it's is true and was a split up from a Good god, or maybe was a lie fabricated by an Evil god to rile him up against the good Gods), or was just fabricated by TDO as propaganda for his followers.