Great point!Knives are even older technology. Is that relevant in a deadly force encounter? That's the nonsense part.
I'm guessing this doesn't apply to an LE officer on duty, but for the rest of us - particularly those who know how to use old technology - a knife may have been preferable in the situation of the video. For some, having a pistol in the right hand would have been a distraction and a liability, a limit to options at least.
Imagine the scene if the defender had a modicum of ablity and a good knife in his hand. For that matter, a fair amount of skill and nothing in his hand.