Not dumbest ever, but I would place it top ten.
He seemed a good kid, folks said good kid. How did he end up running from an alleged fight in a transit station and chased into a park by the police. And if told to drop what he was holding, why would he not drop what he was holding. There was something wrong in that kids head at that moment.
Probably scared... bunch of guys wearing tactical gear, pointing assault rifles at him... probably giving confusing, contradicting orders (as usual).. most people would be scared out of their wits... and understandable might not react exactly how the police would like.
Especially if they were yelling "drop the gun"... "drop the gun". (or similar).. repeatedly.. and the guy wasn't holding a gun to drop. Was the kid even given the time to react?
As for my post being dumb... Is it dumb to want, and expect, trained professional tactical guys to properly assess a situation before killing people?... IMO... If you can't do that for whatever reason... You shouldn't be in that situation.
It should not be 'shoot first, ask later'
Cell phones are pretty small, smaller than most pistols... and certainly not held in the same manner as a pistol. I guess the kid could have pointed as if it were a pistol... but I doubt that very much. According to his family.. He was on the phone when he was shot.
Of coarse, may be the kid did have a gun!?
When blackberrys first came out... I was 'taken down' in a grocery store when a 83 year old man called and reported I had a gun. It was my berry clipped on my belt, center of my back. Wasn't a big deal but afterwards they told me they get these calls fairly regularly.