It doesn't though, it places the Earthen on Azeroth before they were afflicted with the Curse of Flesh, obviously, as they couldn't be afflicted with it before existing.
Titans make earthen from a blend of Azeroths stone core > Earthen afflicted with curse of flesh, become troggs and dwarfs > Curse of flesh was discovered by the Titans > Titans worked on a way to prevent curse of flesh from afflicting future models of earthen > came and had big fight with old gods
We do not know if the old gods were here before the titans or not, we can make assumptions, as you seem to be doing at every turn, but we simply do not know, all we know is that it took the old gods affecting the earthen to alert the titans to their presence.
http://wowpedia.org/Lore_Keeper_of_Norgannon
Also gives a little background into it.