Interesting point the OP is making.
While I have nit watched the clip, healthy people have collateral circulation and two arteries positioned at the opposite sides of their neck that feed blood to the brain, I dont think that applying pressure to the back of the neck without using any hands would cut off circulation, but I havent experimented it either..
I asked a police officer who told me that using the knee is basic academy training, and should not kill anyone.
But as I mentioned, I am no expert and haven’t even tried it.