Because of that what I do is just look and say "hey that looks like stuff from X" and knowing that Guro Dan is very familiar with Wing Chun and he specifically notes Kuntao it makes sense to apply it there. /Shrug.
Perhaps you are correct. There are obviously similarities of motion between a great many arts. I remember watching a Goju Ryu video a couple of years ago and then contacting friend of mine who is very advanced in Okinawan Karate and saying "I had no idea that Karate had trapping like that!".