Sweet, but how does he control it?

From the article:
For Barnes, the device needed to be able to take cues from the human body. The lab designed a prosthesis that uses a technique called electromyography to pick up on electrical signals in the upper arm muscles. By tensing his biceps, Barnes controls a small motor that changes how tightly the prosthetic arm grips the drumstick and how quickly it moves, vital skills for a drummer.

The researchers then added another layer of complexity: a second, autonomous drumstick on the robot arm (see photo). This second stick, controlled via its own motor, uses a microphone and an accelerometer to sense the rhythm Barnes is playing, as well as music from any nearby musicians. An algorithm then produces a new beat with a complementary rhythm and melody, modelled on the music of jazz greats like John Coltrane and Thelonious Monk.

With this extra artificial intelligence, human and machine combine to make Barnes a kind of "superhuman drummer", Weinberg says.

@Zawash

Ok, that's even more impressive.

super rad. looks like issues in swinging and placing notes with particular feels, and for the computer to know when to play a rest, which is as important as playing a note.