The old "friend"

I was slightly confused regarding this man calling me, moreover, knowing my current surname. I thought we lost all track of each other a half of a year ago when he left the police, where we were working as partners. He was my teacher in the police, but when I investigated my first little case on my own without his help when he was in the hospital, he decided to leave this police station and move to another. There, he was proposed a higher position and higher salary, which he liked due to him being a family man. Yes, as far as I knew half a year ago he had a family and two children, so money was a key factor for him. Of course, I missed him for some time before I met Markus, so my life changed so much that I even forgot about him at. 

At all, till now.