Haha! I was wondering the same thing! I asked my brother the same question when we got out of the movie. He replied with it's probably because if they named it the Kung Fu Kid most people would knock it for being a "Karate Kid" knock off.
I guess it was more a marketing name than an actual related to the movie name. Plus during the beginning of the movie wasn't he watching some Karate TV Show and trying to teach himself?
