Not certain, but I think they identify your location from your cell phone. They also ask for arrival instructions when you order— i.e., “Look for the red gate” (or whatever). Of the three times we used them, they got a bit lost once and had to call for additional directions. No big deal. The other times, they nailed it on their first attempt. But we were located at Villa EMM, which is just off the main road in Lorient and is easy to find. So YMMV.
I never did get any mystery pizzas, though. (Bummer)