He did stand up with a knife in his hand, but police didnt start firing at this point. If they had fired while he was standing up because they though he was going to run at them with the knife, that would have been a probable threat scenario.
Since they waited 4 full seconds while he froze and had time to assess that he did froze to their order, thats one pretty obvious trigger-happy case.
Maybe there is something else that the video and the comments doesnt cover about the mentally ill / cop POV ?
The family voice-over was too biased to be worth hearing and contradicted themselves like only victims can ("I think he had a knife in his hand but i'm not sure..." when you see the policeman kicking the knife out of the guy range after he's put down; "he never moved!" just after he backpedalled and stand up kicking his own chair back)
Also I would like to have a link on where you found the police report :P