I think you are right, almost I don't have this guy on any of my skype or facebook accounts and I don't have a gtalk account - I only ever spoke to him once for work. But I do have my contacts synced with google using syncevolution. I just logged into gmail to check if he had a picture there and it shows he uses google+ - so I guess this is where the picture came from. I had no idea syncevolution would download profile pictures.