The guy is awake but not fully awake, this is similar to practices done in functional neurosurgery. Often times they are not playing superbly, but they do it the entire time the surgeons are working near sensitive areas because the surgeons can hear minor changes in how they play that indicates what they are doing is influencing neural operations. For bathroom, they have a catheter in and they would be on a diet prior to the surgery to prevent bowel moments during the surgery

A lot of times for awake procedures they are just asking questions to track understanding and speech generation, listening to hear a thickening of the voice or incorrect word retrieval. When they do this procedure asleep, sometimes they insert an electrode in the brain and listen to the sound of the electrical activity to hear if they are influencing brain function(though more commonly they use micro electrode recording just to identify the right location in the brain)

Disclaimer: I'm not a doctor, I'm an engineer. I just develop tools for functional neurosurgery and observe a lot of neurostimulator placements where they often do stuff like this. Once I saw a guy playing an accordian!