it may just be rumour, how would people know that Shmi was Anakins mother anyway, since ob1 doesn't know and i can't see anakin going around telling people who and where she lives.
i think it was a bit cheesy to say that he had no father, isn't there already somebody with that claim to fame, it would have been a bit obvious to say that his father was a sith or a Jedi (it better not be palpatine) and a bit boring for the father to be some random person. I suppose either way Lucas couldn't win. Although I don't think he does have a father, shame though i think it would have been more interesting if he did though although quite his background would have been?