Is it totally wrong that everyone else is saying ew and I am saying "hmmm, intresting?" There's gotta be something wrong with me, right?
But, I agree that it holds little water as the other possible reasons were not factored out (like a real scientific study should if you ask me on how scientific studies should be done...in my opinion). So, until those factors are factored out, leaving sexual intercourse that did not result in a pregnacy left as the only possibilty, it holds little water in my book. Obviously there are the absorbed and "body killed fetus" pregancies that no one knows about, which could also be the answer. But, until you factor out known pregancies, you can't say it is not from a male fetus that was previously in the woman's body.
Just my own two cents.