In Germany, inmates can be released after serving two thirds of their term. Parole after only half of the time is rare, but can be granted to first time offenders who demonstrated good behavior and are deemed unlikely to commit crimes in the future.
I don't doubt he exhibited good behavior. I'm not sure I believe he's unlikely to commit a crime in the future. I wonder if he thinks he was singled out for something everyone in the industry was doing, and thus it wasn't his fault. He wouldn't be wrong about the first thing, but he would about the second. It's admittedly speculation on my part though.
1: https://www.autonews.com/executives/ex-vw-manager-schmidt-ge...