I'm from Poland originally and I also set my thermostat to 20C. My entire life in fact. Not once did I consider it some virtuous effort. If I didn't read your post I still wouldn't know that it's something special.

Are you sure your roommate wasn't just used to 20C and it felt good to him? I often feel "it's too hot in here" when I have to visit offices with temp set higher.

Edit: I had to check because I thought I'm going insane but 18-21C is recommended by WHO?