That data (AOL search data) wasn't intentionally released so while pseudonyms had been used, no serious effort at fully (or more fully) anonymizing or protecting users had occurred. Here the intent is to be able to produce data sets where individual identification will be statistically unlikely if not impossible (by fuzzing the data), or where individuals can refute the data because there's a statistical chance the data is a lie (probability biased in favor of truth so that the aggregate data is still useful).