With the photo of the wreckage showing the gear down and (appearing to be) locked, this suggests the aircraft had been configured for the approach. Where it went down is still a fair way outside the Goolwa circuit so it is possible the PIC was either demonstrating a stall in a power-on, gear & flaps out config or he had one of the young guys at the controls stall it in that config to show how it reacts. It's then perhaps dropped a wing violently, gotten away from him and with a passenger in the back the CG is too far aft to recover it in the available altitude. A simple stall in the approach configuration has turned into a disaster.
I ran through a playback on FR24 an hour either side of the accident time and the flight's not on there at all. The last recorded flight was on 4/Feb/26 from Port Augusta to Parafield so, for some unknown reason, the ADSB-out was switched off.