No surprise, and obviously it should be. However, privacy law has a long way to go to catch up to common understanding and norms surrounding 21st technology.
... It's easy to imagine the same data being used to establish or disprove a defendant's alibi in a criminal case. In this case, the subject volunteered her data to the court, but it could just as easily be obtained through by subpoena if the court deems it central to the case. The legal rules for such orders have yet to be set, but cases like this one make a huge difference in establishing those precedents. And while today's Fitbit customers don't think of their trackers as leaving a trail of evidence, that could quickly change as courts become more familiar with the devices.