My point is that the officer didn't have to instantly demand that the father surrender his weapon. The man wasn't breaking any laws or committing any overt, illegal act. Given this, the officer could have (and likely should have) simply asked that the father re-sling his weapon in a less 'aggressively tactical' manner.
From what I have seen, law enforcement officers tend to respond to situations with emphasis on their own safety. And I wouldn't fault any of them for doing such. An officer responding to such a call would have no way of knowing whether or not the person walking around with a rifle is doing lawful things or not. It is perfectly reasonable to me that for the duration of his contact with the suspicious armed person that he secure the weapons.
Its silly to think otherwise. Least in my humble opinion.