Uh, because the clip is supposedly of a Choy Li Fut fighter knocking out a Muay Thai fighter...
17yr old KO Muay Thai in the first minute

http://www.tudou.com/programs/view/D9sY9Bi2gHo/

http://www.tudou.com/programs/view/D9sY9Bi2gHo/

Nioce 33secs
the original clip was CLF vs Muay thai....where do you get that the back fist guy was CLF? i don't see it.