Yea, just saw the video and the twitter statement above is correct.
I don't think you can call it an "accident" to shoot someone with a gun instead of a taser though. More like negligent homicide. The chief of police explained that the handgun is holstered on the dominant side and the taser on the other side. I understand this, since you need the most control in the hand with the gun. OTOH, it seems like in a split second situation, it would make it more reflexive to draw the gun instead of the taser. Obviously, that is not excuse, as the officer has the responsibility to use the correct amount of force.