I wonder who was in the right seat? The pictures show one of the boys upfront. I don't know when that picture was taken. The flight path from the beginning doesn't look like autopilot flying. I know there was a second pilot onboard, but was he in the back? Hypothetically, say a pilot was hand flying to give the passenger a basic introduction of flying a plane. If the pilot were to have a medical emergency, it would leave the inexperienced and most likely panicked passenger to try and fly the airplane with autopilot disengaged. Not a good hypothetical situation, but it can happen. In my opinion, there are 2 scenarios that fit the flight path. Either mechanical issue or medical issue with autopilot disengaged.