The issue is that dogs are poor generalizers - it's not that the dog is "sneaky, greedy" etc, but that they have no intrinsic sense of morality or "rightness" and so only think something is "bad" if it has bad consequences. If it has never had bad consequences except with a human in the room, then how on earth are they to know that the rules still apply with the human out of the room? You need to train in such a way that corrections and rewards occur when the dog does not think you are present - i.e. hiding around the corner. Read here https://tr.im/gHn00
I personally owned a Labrador Retriever (read: chow hound) that could be left 6" from a hot dog in a sit-stay for half an hour and not touch it - the word was "mine" and it meant that you don't touch that, even if I am not in the room, even if whatever, you DO NOT touch that. You could leave a plate of food on the floor for hours and not only would she not touch it, she would also keep the other animals (dogs and cats) from touching it.
In all probability, these dogs studied were just not properly trained/proofed before the experiment. With "proofing" to set them up and catch them in the act to give