Why do this?

I'm not blaming the victim in this story; he did nothing to deserve being killed. But, why in the world would anyone block another driver just to fuss at them?

I had a similar thing happen to me last year not long after I got here, though of course without the tragic ending. I pulled out into a roundabout and a driver coming from within the roundabout was upset that I did so. He felt that I shouldn't have pulled out in front of him, I think that he was going too fast. We were probably both wrong. So he honked at me and I finished my left turn, thinking that was the end of it.

Instead this guy followed me for about three kilometers swerving all around me, almost ramming me off the road. I finally stopped in a well lit and populated area, since I had no idea what he would do. He came up to me and tried to criticize my driving but didn't really speak English well enough to be effective (his opening line was "What is driving?", which just confused me instead of insulting me). After kind of stumbling around verbally for a minute, I told him I was sorry and he insisted no, he was sorry and we went on our way.

But from beginning to end it was such a stupid thing to do. Suppose that he was completely in the right, which may be. He did six really dangerous things to get me to pull over to tell me that I had done something dangerous.