I'm more depressed that one of the first things to follow 'cops shot one guy' is 'smash shops and loot'.
It's a hair more complicated. It was more: Cops shoot one guy -> peaceful protest is held -> protest gets aggressive (a natural result of nightfall and long hours, they weren't really doing anything at that point, just shouting louder) -> Cops in vests and cammo disperse protest with tear gas and rubber bullets -> crowd gets violent during dispursal (i.e. throwing rocks at cops while teargas in incoming) -> angry violent people scatter and break things as they go -> once one bit of law & order is thrown out, nearly all of it is.
It's true that people's mental behavior is as binary as it is (if I'm not following that one rule, then I'm not following any of them), but frankly the riot-reaction of the protesters is incredibly predictable, given the action of the cops. It's really not a surprise that the state cops (who aren't using the hyper-aggressive rule-1 police tactics) got peace as quickly as they did.