You accessed privileged information that you were explicitly not allowed. To me, asking you not to look at certain information is effectively the same as putting a password on it, then having you break it. In both cases, the intent of the owner is clear: do not access these files. And in both cases, the actions of the perpetrator very clearly disregard the owners intent.
Your example about accessing a website is not the same. It's pretty clear that the person going to new.ycombinator.com is not stealing or accessing privileged information. There have been separate rulings dealing with whether or not employees can use corporate equipment for personal reasons.
A more analogous example to the case at hand would be an employee at Google/Humana/Tinder selling your private details to a third party. This ruling means that such activity is perfectly legal, even if the terms of their employment state the opposite.
Unless, of course, the only reason the court ruled in favor of this person was that they are a police officer. But I guess we have to wait until the FBI attempts to press charges against someone at Google selling personal details to third parties to find out.