That's not the relevant question. The right question is whether the cop was justified. Even so, it's not true. What the LEO was screaming was, "Don't pull it out!". To which Castile was responding, "I'm not". And he wasn't.
The cop should have said, "Freeze, don't move!". I know, it's a little thing. But this man's life may have turned on that little thing in those few seconds.