Well, that wasn't a "test". You might as well give a stranger the keys to your car and then be "amazed" that your car was stolen. Of course, if it were a "Mac" car, then there would be articles about how the security of the car was so bad that someone was able to steal it so easily. Yeah... riiiiggghhhttt!
Take a look at a more realistic test --
If giving someone a local account gives them full control of the machine, you've got problems. This is more like someone stealing your car merely by riding in the back seat.