Notice how the other normal sized officer in the beginning was talking to the young boys like a human. Then this bozo pint-sized man runs in like a bull in a china shop.
I saw more than one officer running.
I saw the officer you're talking about react in response to circumstances that were not of his making.
As for unholstering his sidearm, the more I look at that video the more I feel like he responded appropriately from his perspective, and I think his training was on full alert. He had quick instinct to protect his person when his immediate space was approached from behind. His training had him protect his person, and it kept him from opening fire in the split second he had to decide whether it was necessary. One more thing about this sidearm, looks to me like he never put his finger on the trigger. If so, it's pure training.