I would only expect a human to think rationally. Maybe ask yourself while in the heat of the moment. "is this dog attacking me?" If you can't do this, then you shouldn't own a gun. The article says the dog "lunged". If this is considered attacking then we have lost all common sense as a society.
I still don't know how to large breed dogs could knock someone down and not bite or shred any clothing and have it be considered an attack. I'm willing to bet the two dogs were wagging their tales and were jumping with excitement.
Again, this owner should have control of his dogs, but the gunmen shouldn't be that disassociated with common sense.
If a Golden Retriever ran onto your property and you went pet it and it bit you. Would you pull out your gun and shoot it? Or better yet, if a Golden lunged at you, would you shoot it? ....I think not. The breed of this case shouldn't even be considered. This was a dumb gunman who was playing god.
Don't want your aggressive dog shot? Keep it on your property.