In the world of electricity a wrong answer might work for a long time before something goes wrong.
Jar546 (Jeff I think) has posted a link to a little boy who was killed from electrical shock. This circuit worked without fail until the tragic accident.
There is no doubt in my mind that the person that made that installation was not thinking about killing someone when he installed that circuit. They probably thought that the installation was done in a proper manner. Without a doubt in my mind the person did it in the fashion that they were taught or done something someone had told them would work. I feel sure that they didn't do anything they thought was wrong on purpose.
How many people do you see on this site that asks if the equipment grounding conductor can be used for a return path? This has been asked here several times and at least once in the past week..