My legal opinion:
The Camaro is 100% at fault for causing this accident. However, you would have to assume that the pick-up was driving at the posted speed limit and no higher. Also, I can only apply the laws of the State of California, not any other state (this video was in NY).
The Camaro violated the law in two ways: (1) using the shoulder/emergency lane in an attempt to pass; and (2) tailgating. He could also be charged for reckless driving given what he is doing on top of the other violations to the vehicle code. The pick-up, again assuming he was driving the speed limit, would have been deemed driving normally, except the one bit where he used the emergency lane slightly to avoid collision with the Camaro.
At civil law, the Camaro is also at 100% fault because he caused the incident by using the shoulder in attempt to pass and then cut off the pick-up while in that position. Whether or not the pick-up should have let the Camaro pass earlier is a non-issue if the pick-up was driving at the posted speed limit.
No matter how you look at it, from a legal standpoint, based on JUST the video, the Camaro was the absolute actual and proximate cause of the accident.
My personal opinion:
At a certain point, you have to recognize that there is some lunatic behind you trying to pass. If it was me in the pick-up, I would have driven faster to get ahead of that one semi towards the end of the video and let this guy go. As you can see in the video, it just isn't worth it to give some asshole some grief. You are legally allowed to drive beyond the speed limit for a short amount of time if you can show that there was some guy behind you closing in and it was reasonably necessary for you to increase your speed above the speed limit to safely move out of the way.