First of all, your link doesn't prove anything. How do you know that woman was white and how do you know that man was black? You don't.
Second of all, I just asked the very same question, although my explanation was more thorough and articulate. Your explanation has a tone of jealousy?
As to the answer to your question, my opinion is the media. Now a days, all the rap songs are stating how all their females have to be thick, red boned or white. Also, black males seem to be under the impression that black females are loud and cause nothing but drama where ever they go, and white females will do anything. Are you from the south. I am, and i find that black males interest in white females is more typical in the south. Then again, the south and the north are like two different worlds. (In my opinion)
personal knowledge and experience