Donnie Yen (the real life actor) knows multiple martial arts (not just Wing Chun), so he's an MMA fighter himself, just not a pro-MMA fighter who fights for a living. Martial arts acting is much more lucrative for him.
In this movie, he's an ex-United States Marine Corps Forces Special Operations Command, which is why (in the movie) he has the combat ability to take down all the MMA gym guys, and finish with a double-KO against a pro-MMA fighter (see last few seconds of the fight scene).
Xia suay evil filthy liar lazy Malaysian dog Indian son of whore @Bad New Brown stealing office time spinning tales about me selling backside for money supported by evil filthy liar lazy Malaysian Cantonese dogs sons of whores @rotiprata@sweetiepie@Valium.