I'll be brutally honest here. Three weeks after I adopted Gambit, he was that emaciated. I provided food. I offered raw, I offered quality kibble. I offered the crap he had been eating. I cooked for him. I went out and bought him hamburgers and chicken nuggets from every fast food joint in a 15mile radius. I put it under the bed, so he could eat after I went to sleep. I fed him at the same time I fed Argon, so he would see someone else eating. I fed him and left the apartment, so he could eat without me present. The poor guy starved himself through stress.
So, yes, it can happen. But you have to do something. I begged Chaz for help. He went to the vet 3 times. Had there been a breeder to contact, I would have been pounding down their door.
The issue in my mind isn't that it happened, because it can happen to caring, loving, dog owners. I would have moved heaven and earth for Gambit to get him to eat anything. But to see it happening and just let it go is wrong.