To be exact, Google says they did not:
- Block the particular offender, because it would leave all others like it intact
- Use sentiment analysis, because it would discriminate any controversial subject
- Begin to expose user reviews for merchants alongside their search results without affecting the search results.
Instead they developed an "algorithmic solution which detects the merchant from the Times article along with hundreds of other merchants that, in our opinion, provide an extremely poor user experience."
Before reading TFA my thought was that they could merely put zero weight on links in reviews claiming negative user experience. But Google's blog post says that was already being done: The review sites' links are rel=nofollow. "Ironically, some of the most reputable links to Decor My Eyes came from mainstream news websites such as the New York Times and Bloomberg."
NY Times article states on page 3 that "Google is intimately familiar with the rage inspired by DecorMyEyes. If you type the company’s name in a Google Shopping search, you’ll see a collection of more than 300 reviews, many of them arias sung in the key of livid." My guess is that they have finally stopped ignoring this information for their search results.
The tricky part is to keep the algorithm not suspect to manipulation by merchants who would write good reviews for themselves and bad for the competition.