Just a note: Many people do not know what aggressive behavior looks like. In fact, dogs are more likely to display aggressive behavior if they are leashed (i.e. protection/police K9 will bark its head off and lunge at the end of his leash when in “take down the perp” mode).
Sheepdogs (this was a chow/belgian mix - note, I rarely trust Chows or chow mixes) tend to circle people, and can indeed bark about it. If the dog was LUNGING, since it was offleash, it would have gotten someone. It was likely circling around, barking, wanting to be chased (i.e. playbowing, often mistaken for “he’s gonna poooounce!”). Agressively or not.
This being said, I totally agree that the mistake was that of the owner of the dog. His dog was supposed to be ON LEASH, and UNDER CONTROL, and for that, I feel little pity for him. It’s sad for the dog who, likely, was just being a dog. The owner put his animal at risk, and that’s a shame.
As a side note on the circling/barking behavior: I have an Australian Shepherd who has such strong prey/herding drive that she, too, circles around people at the park and barks her head off (usually so we’ll, quote “Throw the goddamned ball now now now now now now now now now nowwwwwww!” :D) It gets obnoxious. But that’s what she’s bred to do.
I’m not sure how I would react if a strange dog came running up to me and my (hypothetical) children. My reflex would probably be to tell the kids to stand still and get them out of the “line of fire” and evaluate the situation from there. But then, I’m a dog trainer, so my reading of canine body language is pretty good…
I can’t blame the dad for reacting the way he did. I am, however, reluctant to say that since the dog was loose and running towards him and the kids, it was immediately a threat. I also wonder if he would have shot a cute little terrier if it had done the same thing… I trust little dogs least of all.