I noticed that the grass between the road and power line post is not disturbed and there are no visible skid marks on the road from that direction. This means he was heading toward that direction. The tires are locked toward the passenger side. I venture that he wandered off the right side of the road, swerved left (possibly causing the rear to come loose), then over-corrected right (leaving the wheel locked in the over-corrected right turn position). This is when the rear tires left the road, with all weight bias on the drivers side. The downward slope of the ditch, with all the weight bias on that side, caused the car to over-turn. Certainly, anything could have caused him to over-correct, but, that looks like how it ended.
Maybe we are all wrong. He could have just been sitting on the side of the road, drinking his Pepsi and admiring that pole. A moped may have driven by at blistering speed, creating a shockwave that blew him over.
The way he described it to me, he was rolling about 15mph, poppped the clutch and broke the tires loose. It got away from him and he came around 180 and drifted (slowly) into the ditch. There was such an incline the car rolled (gently) on its lid.
Both the guys were fine, the funny thing is they both cut their hands climbing over the barbed-wire fence.