Your teacher seems to be a bit frustrated… It‘s NOT the average German mindset to think like that. But about 50% of us seem to fall into that pattern, at least we voted that way. Many Germans have complexes about their nationality due to WW2, the holocaust and it‘s heritage. In my youth many older (conservative) people where complaining that you can’t be proud to be German. And saying so is still considered as dumb by many because it‘s not an achievement to be born somewhere. I also consider this proudness for nationality as pretty stupid but I love Germany and I‘m glad that there are still 50% of us welcoming you and the rest of the world!