2nd duan is his rank, similar to how Dan is used to denote the rank of the fighter in Japanese martial arts. Similar to how it is in Japanese martial arts, there are grades before you graduate, and when you finish graduation, you start acquiring the technical ranks. Look up the "Chinese Wushu Duanwei system" to more or less understand how it works. It's a bit complicated but it basically means he's two levels above what a "black belt" (there are no belts in Sanda, but stars) would be. Which means he's allowed to train up to a "black belt" equivalent in Sanda(someone who's mastered all the basics), but can't award the technical Duan ranks (needs to be a 3rd Duan or higher to award the 1st Duan, 4th duan to award the 2nd duan, and 5th duan to award up to the 5th Duan).
The most amazing thing i saw in Sanda however, is that to acquire the Duan ranks you do not need only to master the technical aspects of Wushu Sanda, but also the historical and philosophical aspects. You actually need to write a Thesis on the importance of Sanda in order to move up to the higher ranks, lol.
For comparison sake, most professional Sanda fighters hover around the 2nd to 3rd Duan ranks, some are 4th. There have been many Sanda world champions that are 2nd or 3rd Duan. My cousin managed to qualify for the Brazilian championship but didn't get to the top 3, won the regionals 2 times.