“Like all opioids including heroin, fentanyl is a respiratory depressant – it interferes with the user’s ability to breathe. Because it is so concentrated people can misjudge the dose for themselves to dangerous degree.”

This is why he could say he couldn't breath when he was not being choked. The officers should have realized he was on opioids and administered narcan. His death is still on them. But he also was placed in the cop car and kicked his way out, which is why he was on the ground. That was probably the meth doing it's work.