Well, if you stop your hand movements he will probably provide more clarity about what he wants you to do.
Because the trained professional hasn't provided enough clarity in the first place? Top work by the LEO there.
Also, maybe the LEO should have said 'Sir, just stop moving' That would have worked.
It appears the uniformed officer who initiated the interaction was so scared he couldn't even say what he wanted to say. It's okay though, because the thin blue line that backs him up is happy if he said vaguely and imprecisely what he sort of wanted then shot the bloke for actually doing as he was told, not what the LEO though he was telling him.
Further instruction and communication will follow because the situation can calm down again. You can then make it clear that you weren't reaching for it, but rather your ID.
Or, you know, the LEO could have said what he actually wanted the innocent, soon to be shot dead man to do. Again, with the highlight that one of these two people is a professional doing the job he was trained to do, invested with the authority of the state (or county or whatever)
He can then nervously chuckle as he tells you "yeah, for future reference, Mr. Castile... not a good idea to go fishing around in your pocket area after you've just told an officer you have a firearm. That could've gone really badly. We're trained to react. Anyway... I appreciate you letting me know. I need to secure that weapon before we continue. Please step out of the car."
All the responsibility to be calm and communicate clearly falls on the civilian. I get it.
If, however, you continue your hand movements... he is going to feel like he has no time for elaborate communication and his instincts are going to kick in and he'll reasonably feel that shouting something like "don't reach for it!" (yes, even if you're not reaching for it) should be sufficient to impress upon you that you should stop moving your hands.
Elaborate communication? You think telling someone to stop doing something
they are not doing is elaborate communication.
There's a world of difference between 'stop moving', which is what the LEO should have said and 'stop reaching for your gun' which is what he said. A man cannot stop doing something he has not started doing.
Maybe, if the same consequences accrued to policemen who ********** up like this as would apply to a civilian then they'd be taught to be better communicators under pressure because, you know, that's their job.