It's no fluke. Google "live at Landmark" (a practice Landmark encourages--its domain name is LiveatLandmark.com), and you're likely to get an ad that says "UM Student Housing--Zaragon Place Luxury Lofts." That one links to the original Zaragon, just a few blocks down South U from the Landmark.
Both Zaragon and Zaragon West are owned by a large real estate company in Chicago. However, Landmark is the Goliath in this match. It's owned by American Campus Communities, which owns more than 100 campus-based apartment complexes.
Neither company returned calls about their marketing strategies, but clearly Zaragon is an enthusiastic user of Google AdWords. Its ads are conspicuously placed in what Google calls its "top spot." According to the AdWords website, a top spot is never guaranteed--but your best chance is to bid generously on the keywords you want. To get it, Zaragon must be offering more money for the keywords "Landmark Ann Arbor" and "Live at Landmark" than Landmark is.