I thought planes had to be put into up mode to fly????? LOL
All aircraft have trim control that you set so they will fly hands off. You need to change the trim for differing load weights. Looks like the elevator trim was set just right for a take off without a pilot in it. I reckon the pilot got into deep excreta after the event. It's written instructions that you chock the aircraft before you solo hand start them. There was a lot of run away aircraft back then due to not following procedures. Generally they just carved up some other poor buggers aircraft or property.
I remember that incident well. There were red faces all round.
__________________
PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.