You can believe what you want but I know from experience that there are Japanese people that enjoy spending time with foreigners only because they think they're cool.  It's like hanging out with a movie star.  For other Japanese people, foreigners seem interesting but very different and a bit strange.  This doesn't come from racism or prejudice but simply ignorance.  There just aren't that many chances for them to get to know people that are not Japanese.  So, is it that far fetched to think that a woman would date a foreigner to look cool to her friends?  I don't think this happens very much but it's not as far fetched as you might think.