And the answer is simple, God created the something in question that eventually gave rise to the universe. Remember, their universe was multi-leveled. This level is simply an edition to the higher levels where the God was believed to dwell.
The God created everything and the God has always been around, creating this and that for an eternity. Everything links back to the God. Take for instance man. Where did the dust of the earth come from? It came from the God's spoken word followed by the God's own breathe of life. The man came from the God. Where does the man go from there? "The soul goeth back to God that giveth..." It's circular, from the God back to the God.
When I say reason through the mythology, I mean reason through it according to it's own standards. This is sort of like the Protestant problem with Catholicism. They accuse the Church of traditions which have no basis in scripture. That's the point of the Protestant Reformation. I see the idea of creation ex nihilo as one of those traditions which lack scriptural support when you investigate very closely. And I think it would do the world justice to always question anyone who ever comes along promoting religious or even scientific claims based on "nothing" and "nothingness." They are deceptive ideas. And a strong truth seeking path will veer away from these various fallacies...