"Stick" miss- read.
I still think my point stands though. Now not only must the dog know when there is a threat, but also know how to do the absolute minimum damage mitigating the threat? Are we asking too much?
We've probably all heard stories of the family dog growling when a couple gets in a fight, and makes them back down. Those dogs clearly know both people, but feel that they must control the fight. My dogs have only met my extended family a few times, they're not going to treat them as "family" when they come into the house or yard unannounced. (mine will just make a lot of noise though!)
Besides, how many times recently have family members killed the rest of the family? I can think of three quickly. If the uncle presented himself as a threat (mask, prop weapons or inciting panic) vs joking around, "I" would want the dog to react that way, and quite frankly, continue until the threat was subdued or called off.
Where were the owners to attempt to call the dog off? If it was a dog, a "threat" and some kids, it may have thought that was the only way to control the situation. A terrible situation to put the dog in, but I can't see how the dogs reaction could be faulted.