All air carrier flights are flown from shortly after takeoff to some point in the approach phase on a clearance that is entered in the flight management computer during pre-flight. Until the initial unplanned left turn the flight was likely flying in this manner. The turn itself could not have been executed on autopilot though. It was far too steep. The autopilot flight envelope protections would have limited the bank angle at that altitude. As it is, the plane was likely riding a fine line on the edge of a high altitude stall/spin scenario in order to execute that tight maneuver.

Might be wrong, but the left turn I believe you’re referring to happened when the plane left its planned flight path, at which point it descended to 23,000 feet and flew over land.