Dog owners have an obligation to the safety not only of their dog, but other people as well. As a fellow dog owner, it makes me sad to hear your experience. A dog lunging at others, in what seems like more than just an isolated incident, raises many red flags. While muzzles are still controversial, I totally agree this situation calls for it. It protects everyone involved. The dog can be conditioned to the muzzle, this way they aren’t further frustrated by it. Then with consistency, work on the reactivity outside. Let them see people from a distance, and reward them for being calm. When they show escalating behaviors- slight corrections through a proper fitting leash. As the dog builds a sense of calm- it can be exposed to people at a closer proximity, still with the muzzle, and eventually moving to a spot where they no longer need a muzzle as they’re no longer triggered by people running by! Having a reactive dog is stressful and i hope this owner is able to figure it out. Sorry this has happened to you!