Well there are two basic definitions ..one that is based on an overall sense of right and wrong -which can be subjective, and is more fluid, and another that pertains to the rules and regulations governing a profession.
I view ethics more as an (admittedly subjective) adherence to doing what is right. Ethics supersedes the law IMO, and while the law often mirrors what is ethically right or wrong, and often serves as a guideline, and in many cases seeks to define ethics, it is too absolute and inflexible. I cannot think of a good hypothetical, but there can be gray areas where the more ethical road could potentially involve not following a particular law. In general not breaking the law is ethical behavior, but in those gray areas where following the law goes against your sense of right and wrong, or where the law itself is unethical (as you yourself admit can be the case), then it is possible that the ethical path is NOT following the law.
The article did kind of define ethical as the subjective definition i am using when it mentions lying and cheating, and from the experiments conducted and questions posed (granted I am not referencing the actual study) such as cutting off other cars, or not pointing out a cashiers error I also get the impression that they were driving at the former more subjective definition as well.
YMMV