I've driven past this site a few times and had a look-see.

He was northbound on SH2 - click here for a look at his track;
http://goo.gl/maps/c7Ro

He has passed by the letterbox on the left in this picture without hitting it, so he was well on the road.

Now continue along the road in the same direction a few hundred meters alongside the line of trees, and you will see a vehicle entrance on your left with white fence railings, here http://goo.gl/maps/j3F9 There is a white car parked down the driveway somewhat. There is a substantial impact mark on the side of the driveway, halfway down into the drain.

The rider appears to have simply wandered off the road and half way down the ditch, and hit the driveway harrrrd on the full, catapulting him and the bike skywards. I cannot see any reason for this, except maybe he had a medical problem, or perhaps he discovered himself in the gravel, and wasn't willing to steer the bike back to the road.

In any case, it's a really severe hit and I hope he's ok.