What do you know that everyone else doesn't Cake? Other than OP saw a dog in a car with a blanket we have no other details do we? Not even breed. We don't know that the dog is kept in the car all day without contact, food, water, stimulation do we? We do know that if it was left home all day it wouldn't have contact, stimulation or possibly have the door left open for toilet breaks. What is more likely to happen is the dog gets bored and owner comes home to a half chewed house.
Penelope thank God you are not my dogs vet! My dog refuses food until 6pm. OMG! Id better check him for bloat. I've obviously been doing it wrong for 6 years. Over 20 if you count previous dogs that have been fed once a day - On vets advice. My vet must be a right arsehole!! My dog, however, is correct weight for height, has 4 walks a day, knows lots of tricks (so is appropriately stimulated), does agility..... He prefers to be outside during the day - even though the back door is left open so he has a choice whether to be out or in.
When he comes indoors he prefers to be out in the conservatory rather than a centrally heated house. And is much more content if I leave him in the car for short periods than he is home alone.
Again I suggest OP finds out details of why the dog is left in the car, how long he is left in the car, how often he gets water and toilet breaks BEFORE she reports someone she doesn't know and has no idea what she is reporting.
If she were to behave like a concerned adult surely OP would ask the owner some basic questions and if not happy with the response let her know that if the dog is in the car tomorrow she will be reporting her. That's how adults usually work - rather than being a faceless trouble maker.
But I very much doubt OP will come back to this thread and admit she got it wrong and the owner makes sure the dog is adequately catered for during her breaktimes. In fact I wouldn't mind betting she will be back to say the dog wasn't there today because it froze to death yesterday ;)