Well according to our understanding, on stories like these they usually embelish on the 'origin' part. In the case of the bible, the story of the archangel gabriel visiting Mary is number one on the suspect of being an embelishment.
And speaking of being 'historical', as in written down by a witness, there are things in the bible that strikes me as 'filled in'. I only go to church during easter, so it I had it read to me very recently.
Like the story of Jesus praying in Getshemane, it was supposed to be jesus' personal prayer, who witnessed that?
Or Jesus personal discussion with pontius pilate, again, who wrote that down? Maybe someone interviewed pilate again later, I don't know, that doesn't seem too plausible, as I never heard the name pilate written down again as one of the accounts.
Or when Jesus got tempted by the devil, again he was supposed to be alone. Did he tell his disciples afterwards, or is this completely creative writing (or oral as the first christians did it)?
These are just some of the thoughts I had while listening to the sermon. My point is I think that there was some artistic license in the whole mythology of Jesus. Maybe 'to make it flow better' or something like that.