Unless the video was edited the chokehold was just used to get him on the ground. Control the head you can control the body.
That approach works a whole lot better, and it's a lot safer, if you have a guy do it who's not a foot too short to keep his feet on the ground at the same time he's applying the hold. You're not really controlling jack if there's no leverage, it's just the force of the smaller guy's body weight hanging around the bigger guy's neck. You're just choking the guy out, and that just has 'way too much potential to go wrong in a big way.
Beyond any issues with cops, and addressing human male stupidity in general, for some dumb-as-a-box-of-doorknobs reason, the whole 'Choking out' deal in a physical confrontation has become a 'Thing' with dudes in recent years. Maybe it's the influence of MMA, and God know those guys are a bunch of philosophical rocket scientists every guy ought to be taking his lead from, but while it usually works as intended, there are a ton of times it ends very badly, in my professional life I recall reviewing several totally unnecessary death cases where people who thought they knew what they were doing turned out to be wrong.