I invite everyone to take a close look at the accident scene photos and at the map. He lost control and slid off the West side of the road, the side without a guardrail. It was the outside of a turn and that's a pretty normal place to go off the road, taking a turn at too high a rate of speed. You can see that when he hit the dirt one of the wheels dug enough to be torn off and the car flipped. It's down a bit of an embankment so it's not that surprising for it to flip but he would have been going pretty fast to tear that wheel off like that.
So he's crashed and he's injured but he manages to crawl out the window, leaving his phone in the car. He climbs up the embankment to the road but he doesn't wait for a car to come. He doesn't follow the road, continuing the way he was headed. He crosses the road, climbs over a guardrail, descends a steep forested embankment and falls in the river? Seriously, if you haven't looked at the street view I encourage you to do so. One wouldn't just step off the road, fall into the river and be carried those several hundred yards. It would be a climb to make your way down there even for an uninjured person.