Island Man:
A dog some great distance away at "ground zero" (too far away to be in your hearing) heard the sound of an ambulance siren or some other sound produced by some kind of equipment or machinery. The sound of this equipment or machinery was interpreted by the dog as being the sound or howl produced by a very large and vicious alpha male threatening to attack.
Indeed. And you know what also sometimes generates noise resembling howls... wind. It is unremarkable that howling wind might set off dogs howling. Nothing to see here.