I don't think anyone involved with the case has said that the boy pointed the gun at the police. Even from the earliest reports it was that he was told to raise his hands and instead he pulled up his top and showed them the gun.
The officer in question was apparently new to the job (no excuse really but it's relevant) and by the sounds of things panicked and rushed into a situation. Certainly by all accounts in the media so far the dispatcher had not told them that the 911 call said that the gun was probably a fake so he's only going to go by what he sees in the moment.
I would suggest that yes, procedures have not been followed correctly (as mentioned earlier the squad car doesn't exactly approach at a safe distance and sensible speed) but again, I'm not sure I would have handled it any differently. I do not believe that all police should accept the risk of getting shot in the same way that I do not believe that all black kids are criminals. HOWEVER - the fact remains that the boy went out in public with a realistic imitation firearm and was seen waving it about IN PUBLIC causing sufficient concern that a member of the public call the police. In a state with a high incidence of gun crime and a growing problem with gang activity.
This is not a clear cut "the blame is all X" for me. If the cop got shot he would just become another statistic of gun crime in America (regardless of his ethnicity). If the gun had turned out to be real - likewise. The fact of the matter though is that the gun wasn't real but the kid was spectacularly stupid in what he was doing. Equally while the perceived threat was high the police did react too quickly. It's very easy for us all to sit in judgement on the other side of an ocean sat at our keyboards but the fact remains that this kind of incident happens all too often in the US. That kids family has been devastated and the police officer will have to live the rest of his days with what he has done playing on his conscience. The part that REALLY mystifies me is how the US public and government will still refuse to see that they HAVE to address the issue of gun ownership and the culture of guns and gangs in everyday life or this will continue to happen all over the country.