[Jeff Higgins]

According to the driver's own comments (accessible by clicking on the "read more" button in the video description), he had lost the brakes. Pedal went to the floor, and as a result, his pants leg caught the gas pedal. The weird throttle modulation is a result of him frantically pumping the brakes while his pants leg was thus hung up on the gas pedal. The big rally style handbrake was linked into the main braking system, so pulling on it did no good either.

He says he knew there was no way in hell he was going to make the corner without somehow trying to scrub speed. He put it into the ditch on the left in an effort to do just that. Didn't work out as planned, obviously, but he goes on to say that missing the next corner (which would have been inevitable at that speed) would have had far worse consequences, with a much higher drop-off until his first hit down the hill.

The driver made a split second decision that probably saved his life. He does a great job of running through what happened and why he did what he did. If you read that first, then watch the video, it all becomes quite clear. He didn't miss the corner, he wasn't trying to hang the rear end out, he wasn't trying to drift it, none of that. He did, in fact, deliberately turn too hard into the corner. He also leads into the description by saying PLEASE READ BEFORE COMMENTING! (his caps, not mine).