The river they said they were visiting runs through a mountainous area that has varying terrain ranging up to 10,000ft.
It does more look like the aircraft was struggling for performance due density altitude and hit a downdraft or similar that overcame its limited capabilities.
Looking at the footage and especially the slow motion and rear seat footage its absolutely amazing anyone survived let alone was walking around afterwards. Reminds me of the footage of the bonanza hitting trees whilst scud running through mountains and getting away with it.