Just curious because it seems like he should have gotten about +4 (as I got -4).
Nevermind. I overlooked that he's only played 12 games at this time control. But still!
The higher your rating deviation is, the more rating will you win/lose every time you play a game. It is to compensate for the time it takes to grind up a new account, and to find your true rating faster than, let's say, make Magnus Carlsen play 200 games or so, just to get 2800. If you had beaten that guy, he would probably have lost 50 rating.