Seems ~20% of the population are immigrants (https://en.wikipedia.org/wiki/Nuremberg#Demographics), some of the people you saw are Germans and some of them are not, but I think the main confusing part is how you mix up how someone looks and what nationality they have. I think maybe you're trying to say "white" instead, but for some reason avoided using that word?
French people, Slavic peoples, and Irish people living in Germany do not become ethnically German because they are white, and it's obvious that in any nation-state it would be reasonable to be surprised if the vast majority of people were not members of the ethnicity that formed the nation-state.