I believe cutting off the flow of blood to his brain was the reason he died.
The autopsy does not support your conclusion from watching a video.
He was not strangled. That means the blood supply to the brain was not cut off.
He was not asphixiated. That means his air supply was not cut off.
Videos can be very misleading. The narrative was put out from the first that the officer killed him, with all kinds of conclusions which could fit the video, but without any potential alternate possibilities, which also fit the video.
Once the narrative is established, it is very hard to alter the first impression planted in peoples' minds.
The blood was not cut off to his brain.
With no blood flow to the brain, you lose consciousness in seconds.
The autopsy says you are wrong, but hey, you watched a video, which tells you more than an autopsy.