He didn't get electrocuted. He got burned by the flash. This is what's called metal-clad switchgear. It's a circuit breaker that "plugs" in. He was "racking it
out", turning a handle to slowly "unplug" it. It's supposed to be denergized first, but just like if you pull a plug out of the wall when your appliance is still on and you draw an arc, these will draw a very large arc if you don't turn them off first. The dangerous thing about metal-clad switchgear is that the connections are in the back of the circuit breaker, so you cannot 100% tell that they are in the clear before you remove it. You have to depend on an indicator window that sometimes malfunctions.
That's likely what happened here.