Google is very helpful (/s) and holds on to stuff you don't need forever, it was probably on an email trail at one point. You may not have known it, just a .cc or something but Google stowed it away for you. I still have names and addresses pop up from the old Google+ days, they are just there and don't go away. I never saved them but they must have interacted with me or I them.
I could be very very wrong but it's not out of the realm of possibilities.