Did the officer testify? I did not follow the trial at all, so I do not know. Did the officer mean to say "don't move" but actually said "don't reach for the gun?"
The clear issue here is that regardless of whether the subject misinterpreted what the officer's commands were and regardless whether the officer meant to say "don't move" but said "don't reach for the gun" castile still made deliberate movements to something which the officer knew posed an immediate deadly threat risk to himself and others. Compounded with the fact castile was impaired, and has a history of being investigated by the police (vehicle stops) means that castile's actions may have been purposefully made in order to attempt to cause violence on the officer(s).
To me, having not seen anything in the trial, it really paints a clear picture of reasonable doubt of the officer's intention to feloniously kill castile, but rather the officer's lawful reaction to a deadly force threat.