So wait they do give you multiple Miis at the same time then?
They only give one at a time. Most of those girls must have actually been nearby. Btw, apparently it is actually possible to tap into the streetpasses of distant Nintendo Zones by changing the MAC address of your wifi, or something like that. I met a guy who was using a phone as a wifi hotspot and by changing something he was able to trigger a bunch of streetpasses.