Even if the owner (or guardian, in this case) wasn't responding quickly enough, that doesn't mean the officer needed to shoot the dog.
I hate it when dogs get punished for their owner's (or whoever's) stupidity.
My friend has a pug, and he was attacked one day by a Pit Bull. The Pit Bull was "conditioned" or whatever for fighting. Unfortunately, because his owners were idiots, he had to be put down.