I hope this preacher's message didn't rely on this 'fact' too much. It's simply untrue! Blood types are determined by both parents, neither having more of a role than the other. Besides, Mary being a virgin or not has nothing to do with who the father of this particular child was: it may show that there wasn't any chance of anyone else being the father, but it's not required. She could very well have had other children previously, and still have had Jesus as the direct result of divine pregnancy, with God being the (only) father of the child.

But I'm glad preachers feel free to tell us all about the inner workings of the universe. I'd like to know more about the day the sun stood still in the sky, too, and how it indicates that the sun (and all things) revolve around our perfectly spherical planet. (Go look up the case of Galileo vs. the Holy Mother Church.)