I wrote an article about the purpose of the game. Why it was built. you can check it out here if you like: http://news.ycombinator.com/item?id=4805229
As such I doubt it has much to do with Google Glass specifically - more likely I suspect they're tracking people walking around as they play to build a massively improved pedestrian-route database for a new pedestrian (and in-building, for places like malls, museums, etc) version of Google Maps: http://www.reddit.com/r/Android/comments/138res/google_launc...
Also how long until players must visit Brand X store as part of the game. Probably won't be so obvious, but say a target is right next to Brand X store, and then gameplay pauses for 15 minutes.