Similar things have happened with my cell a few times. Once, my sister called and left a "happy birthday" voice mail. She got a return call from a confused woman whose device showed a missed call from my sister, and who had received the voicemail in my stead. Weird.

I thought perhaps it could be incorrectly entered MSIDs because the calls always seem to be mis-routed to the (theoretically) correct geographical location, but I know nothing beyond my personal experience.