Board Thread:Warhammer 40k General Discussion/@comment-25618639-20150807010020/@comment-25177957-20150810054829

He was born with such powers due to the thousand or so neolithic shamans who sacrificed themselves to allow the Emperor's soul to be born. You might have been reading something wrongly.

As for that Lexicanicum article, the "Emperor" might not have refered to the Emperor of Mankind, but also, the Emperor had powerful psychic abilities before the Dark Age of Technology, yet he slowly learned them over time. So RT canon on the Emperor before the Unifcation Wars appears to still be what most 40k fans consider true, also, this was simply an account or perspective.