Wow that was an extreme reaction (on their part). It's awful that people think it's ok to leave a dog in a hot car.
I think the employees are told to stay out of fights, just like they aren't supposed to confront shop lifters. It's also possible they didn't do anything because there was a story about a walmart employee getting fired for calling the cops about a dog locked in a car.
Wal-Mart Worker Fired For Calling Police - Business Insider