Board Thread:Warhammer 40k General Discussion/@comment-25618639-20150807010020/@comment-2093048-20160203062609

"‘At the dawn of the great diaspora, the Emperor travelled here [to Molech] in humble guise and found the gateway to a realm of immortal gods. He offered them things only a god-in-waiting could offer, and they trusted Him. They gave Him a measure of their power, and with that power He wrought the science to unlock the mysteries of creation."

That's a direct quote. I have to go with Megarachnid's assessment. It seems to basically be stating that the Emperor was already god-like ("God-in-waiting") before he bargained with the chaos gods, but the gods gave him "the power of creation" (which, in the context of the story, most likely refers to the primarchs).

Of course, that's assuming it isn't a lie, which it very well may be. But without proof, you can't just assume it isn't the truth, either...