It's an old trick by street photographers who use wide-angle lenses. It's one i employ a lot, but sadly exaggerated in the ad by targetting scantily-clad women subjects (which I purposely avoid).
Even a 28mm standard wide-angle can be used (in fact, it's one of my favorite street lenses). Most strangers I shoot don't even know they were in the frame. By avoiding eye contact with them (before and after the shot was made), I further enhance the illusion that I did not take a picture of them. :wink: