it looks like they were trying to taxi and turn left (ie left pedal in) and the nosewheel lock was engaged, when the noseweel lock was taken out, the wheel "flicks" to the left quickly (you can see this in video if you look closely), as a lot of left pedal was already applied the aircraft started to rotate left quite rapidly.
like with any pedal/rotation scenario, once an aircraft has completed one or two 360s the pilot will be so disorientated/surprised/frozen in terror... in most cases it's "game over"