I'm confused. Sorry. I'm not understanding what you wrote that you saw the dog in distress yet continued to your car while watching another passerby show concern to handle the situation yet doubling back in your car to make sure authorities were on the way?
Let's face it, we're all different and that's a wonderful thing. I fully embrace it. I've been so fortunate in my life so far that I have never come across such cruelty. I really love the show "What Would You Do" and this very scenario was secretly taped. I was appalled that a group of firefighters ignored the ultimate safety of the dog locked inside. This was a controlled experiment as the car was outfitted with a small a/c unit and the dog handler was hidden on the floor of the car so she could direct the dog to bark also to get attention. But, should I ever find myself seeing anything like that my instinct would be to get to the nearest phone, I don't have a cell, call the proper authorities, get some water, break the window and help the animal. If someone else were on the scene, I still wouldn't leave until I knew the animal was taken care of properly and safe. I don't even want to think how upset I'd be to find a child left like that. The show did that too.
Where I live there's cases of kids left in the cars all the time only to die from the extreme heat. It's heartbreaking.
Twitter shame is the least the owner may face. I hope he/she was cited and has a court date. If the owner is willing to treat their pet that way, what must they do in the relative privacy of their own home. Yikes!!!