Board Thread:Warhammer 40k General Discussion/@comment-25618639-20150807010020/@comment-5880884-20150807070436

Probably a mixture of both. It was not stated that he struck a deal with the chaos gods. For all we know, he only entered the warp gate, where he could have stolen/won power from the gods.Also, even before that he was already very powerful psychically, so perhaps the Rogue Trader info is still accurate. In any case, its very common for GW to publish conflicting canon info, so we won't know for sure.