I'm not qualified to decide whether this statement is true from a factual perspective. But if it is, then we're basically just having a culture war over a fundamentally lost cause set of facts.
This is correct.
The kid could have thrown the gun away at any previous point during the chase, such that the cop didn't see the gun on him or could have actually seen it leaving his possession. He could have stopped running and put his hands up without turning around. I think either of these actions would have dramatically reduced his chances of getting shot. The problem is that identifying these actions require thinking about the problem, something it isn't easy to do in the heat of the moment. They also require optimizing for not getting shot, as opposed to escaping or avoiding legal repercussions, and it seems very likely that these latter two goals were what the kid was actually going for.
These split-second tactical details are dwarfed by the larger issues: don't join a gang, don't engage in gang behavior, don't engage in criminal gunplay. All of these activities dramatically increase one's chances of getting shot, and not just by the police either.
On the Cop's side, the split-second option is to shoot or not shoot. Shooting can result in saving one's own life, or ruining it. Not shooting can result in being seriously injured or killed, or saving one's career. This decision is made in a split second, in bad visibility, under extreme stress of the suspect's devising, with multiple known facts weighting in favor of shooting: the suspect is an active shooter, the suspect was visibly armed seconds ago, the suspect has been actively trying to escape. The suspect is now taking very rapid action which is ambiguous between surrendering or opening fire.
But of course, there are larger issues at play here as well. Why chase the suspect so hard? If the cop had just run a bit slower, none of this would be on the news. Just run a bit slower, let the shooters get away, and then shrug and say "welp, couldn't catch them, darn it." Lil Homicide continues shooting at people without consequence, and the Cop gets his pension. Best of all possible worlds, no?
The Cop, of course, doesn't get this. From my perspective, that officer was doing his job to the best of his abilities. He engaged an active shooter, tried to arrest him peacefully, and then tried hard to save his life immediately after shooting him in perceived and entirely plausible self-defense. In other words, he's a fool who drank the kool-aid, invested in an ideology that no longer exists, futilely trying to hold back the inevitable consequences of decisions made long ago. So he gets to suffer, and others get to learn from his cautionary example. Hit the donuts a bit more, and the shoe-leather a bit less. Tell your kids to go into accounting, or learn to code, anything but policing. Move to the burbs, and let nature take its course.