That sucks...that dude in front was way hard on the brakes and totally slow going into corners, and the dude behind him was not thinking.
He was a lot faster going into corners than the guy in front (although he didn't know it at the time) and was behind and on the outside of him going into that turn. The slower guy braked hard, the buy behind caught up very quickly, and this put them in contention for the same piece of tarmac making that turn at different speeds...the faster guy on the outside then had nowhere to go, and started turning when he had to at his speed instinctively, taking them both out.
The faster rider should of been on the inside of the dude going into that turn, not the outside. Secondly, he shouldn't have assumed that given the straight line speed of the rider in front, that he would be holding the same corner speed.