Nicolas King frequently sings with the Watchtower Chorus and had a supporting role in the DVD released at the 2014 convention. (He's on the bottom row, second from the right.)
But he also is a jazz singer, traveling constantly performing at concerts, casinos, charity events, even a brief appearance on The Tonight Show. (Not much time left for service and meetings, now is there?) Besides that, he's hobnobbing with loads of worldly people, showing off on his Facebook page.
So why is Sergei from the convention video not allowed to play his violin, but Nicolas can pursue his worldly career and get rewarded for it by the organization?