If you've never changed the BSSID from the default of "linksys," my guess is that your daughter's friend's laptop actually attempted to connect to someone else's router. I had that happen to me just a couple of weeks ago at my brother's house.

Everywhere I go I find unsecured wireless routers advertising themselves as "linksys." Comes in handy sometimes. Your daughter's friend may have actually found a neighbor of yours smart enough to secure his router but dumb (or inconsiderate) enough to leave the BSSID at the default . . .

Um, please don't take that the wrong way

PS. If you haven't changed your BSSID, do it.