That ain’t no crop duster. Banking hard at slow speed? Not enough lift and stalled?
That still was the airplane already in the stall induced snap roll. The entire video shows a very high AOA in level flight before this still captured the spin.
From the video it looks to me like they got too slow which induced a stall. This developed further into a spin.
The single frame with the deep bank angle shows the beginning of the spin.
I had Kathmandu on my bucket list before COVID, I’ve read that the airports are some of the toughest in the world to land a plane.
You may be correct, they had requested a runway change and likely banked harder to come around... and fell out of the sky.
That is what it looked like to me.
The pilots should have engaged a go-around procedure for safety.