Well, BSSID, not the easily-changed ESSID (as commented below.)
Presumably some manufacturer of ultra-cheap wifi gear isn't properly setting a unique BSSID range into the units they make, and some stolen-phone operation has the same BSSID as these folks do.
You maybe getting the point there. This incident sounds a lot like an inaccurate Wifi locating result.
Or someone in a large stolen-phone operation has been using a randomly picked MAC address to confuse the Find-My-Phone softwares. That's a lot easier to do.
I bet someone at Google or Skyhook could look into the Mac address to see if there are any abnormalities for that particular one.
I really hope Sherlock Holmes will be there to resolve the mystery.
I took my router with me when i moved back home from university (and i changed the SSID first thing). For about a year my iPad would think it was still at university, and sometimes when i used it to chat with friends on Facebook they would reply "Oh, you're back in town?? Come visit!".
Presumably some manufacturer of ultra-cheap wifi gear isn't properly setting a unique BSSID range into the units they make, and some stolen-phone operation has the same BSSID as these folks do.