He was freaking out beyond what is normal before they ever had him on the even out of the car. It's because he was high as balls. As someone who has been high before on more than one occasion, being high can make unsettling situations absolutely terrifying. That said, the knee to the neck was absolutely no doubt a contributing factor.
But a sober healthy person would've lived because while his breathing may have been more labored, as it often is when someone is on top of you, he could definitely at least breathe because if you've ever truly had your airway constricted being able to speak at an audible volume, much less repeatedly yell "I can't breathe" is pretty much impossible. But there is definitely no reason a cop should ever put their knee on the side of someone's neck regardless
How much panic is "normal" when approached by police officers?