Ditto in the background???

a glitch or intended troll

This has happened to others, there is another questing like this on this sites Q&A section. Something about he might be around that area, or it's just Niantic having fun with you, can't remember.

Happened to me as well a few days ago... proof :

I've had it on a number of occasions over the last month. Think it is just a glitch

Happend to me twice yesterday.

Whatever you do tonight,
Do. Not. Fall. Asleep.