According to the man's family, we aren't getting an independent evaluation. Even if they were pressing so hard to cut off breathing (which it doesn't look like, note that the head is not twisted like with George Floyd), two minutes shouldn't be enough to fry his brain. I strongly suspect this is an excited delirium death.
Are you saying if he had never encountered the police, he would have just dropped dead on the sidewalk at the same moment anyway?
We don't know, we don't have good data on what happens in these cases. What appears to happen is the body is put way into overdrive (note the nudity--this is a common hallmark of such cases. The body is in overdrive, they overheat and they strip off clothes to cool down) and then when the come back down the system swings too far in the other direction and the body shuts down--they die without apparent cause. In the old days it was figured they died of the beating they got with nightsticks in an effort to subdue them but as we have captured more of them without the heavy use of force it looks like sometimes they simply die.
Note, also, that simply being arrested could have aggravated the problem. The stress would have pushed an already-overstressed system even further, thus increasing the chance of a lethal rebound.
Or it could have been the arrest itself caused a death.