The owners not recognizing the signs is a particular peeve of mine. And since many of the attacking dogs, no matter what the breed, are running loose, how is an owner to know what the dog will do when the owner is not with it? Not understanding that their dog, who somehow gets out of the yard or off the leash, is now perhaps in a situation that is frightening to it and might cause it to react defensively is how we get those, "oh, he wouldn't do that" reports.
I have neighbours who thought their husky mix dog was submissive and retiring with all people and dogs she met. And she was, when the adult owners were with her. But when the grandchildren visited and took the dog down the trail for a walk, without the adult owners, she was a completely different dog. That dog was upfront to meet everyone she encountered, human or dog, and I believe she would have bitten if she thought she had to defend those children.