It's not his fault if the biker cut him off and slammed on the brakes.
But...that part of the video you chose to ignore so I wouldn't expect you to understand that.
You and Dari either ignore parts of the video or watched something completely unrelated and just don't have a clue.
Which part is that? Unlike many here I watched every instance of the video and I see the bikers trying to communicate with Lien before the accident. Do you see that? Yes, a biker did brake-check Lien and, yes, Lien probably feared for his life. I am not arguing any of that. All I'm saying is that he could've handled this better. Unlike Ichinisan, I would ignore the bikers running parallel to me UNLESS they're trying to get my attention. My primary concerns would be those in the front and back. If someone is trying to get my attention and then he goes in front of me, common sense would say for me to slow down. I wouldn't go at the same speed or faster, but slow down because this same guy just tried to get my attention.
After the accident, the biker was obviously angry. It's ok for him to vent. The worst thing you can do is show indifference. Lien did that by not rolling down his window. I seriously doubt that if he rolled down his window the biker would've attacked him. But he didn't so it made the biker angrier.
The last time I got into an accident was years ago near Cornell Medical College where I rear-ended a minivan on an icy street when I failed to slow down in time. This was 100% my fault. First thing I did was get out of my car and go to the car in front of me and ask if everyone was alright. I then apologized. I made no excuses, just apologized. The guy, who had his wife and daughter in the car, said they were fine and said everything was ok and he left. No police was called and no information was exchanged. If I started talking procedure I am sure he would've 1) gone along with it and 2) gotten upset as well. But all it took was some common courtesy and apologies for him to look the other way. Instead of treating the bikers like aliens from another planet, Lien could've acted in a similar manner and none of us would've heard about this.