I didn't investigate this like you did, but the first thing that came to my mind was: someone probably called a wrong number. It showed up on caller ID. The recipient of the phone call probably dialed that number when they saw that they missed a call. There was probably no answer. The other recipient sees that he missed a call from that particular number. There was no voicemail, so he probably called that number to see who it was. This may have repeated a few times until finally the two callers spoke with each other and one probably said, "oh...this isn't________. Sorry. I must have the wrong number". I've had this happen to me more than once.