Worse still, it seems likely that they were using data that wasn't actually public:

Their paper reveals that initially they designed a bot to scrape profile data, but that this first method was dropped because it was “a decidedly non-random approach to find users to scrape because it selected users that were suggested to the profile the bot was using.” This implies that the researchers created an OkCupid profile from which to access the data and run the scraping bot. Since OkCupid users have the option to restrict the visibility of their profiles to logged-in users only, it is likely the researchers collected—and subsequently released—profiles that were intended to not be publicly viewable.