Event stress changes time perception. My instructor has a shooting simulator, very cool, and he demonstrated reaction shooting, laying about 5 shots into the hypothetical perp in maybe two or three seconds. They train on minimal trigger movement to get very fast repetition. The trained response is to keep shooting till the target stops moving. So no, the reported sequence does not surprise me, including the shouting. Ten seconds can be a long time when you think you might die. So this reaction is exactly what I would expect given what I have just learned about the training. If there is fault to be found, the training itself should be reviewed. Because that’s the tape that plays when you’re running on pure adrenaline.
Ask your instructor if the kid in this case dropped his plastic pellet gun after the second shot but was still moving, should he keep shooting until he quit moving.