[deckar01]

It looks like he fell backwards, implying the car hit him, but the bodycam actually detached. Until another bodycam shows why it fell, the car either clipped his vest or he pulled it off while drawing his gun…

[fabian2k]

It's not a bodycam, he had his smartphone in the hand and was filming with it.

[deckar01]

I see it in the reflection of the car now. He is holding a phone out in front. That makes it less clear how close his body actually was to the car.