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?
Not sure what you are babbling about but, It's about ethnicity and not race. Plenty of third generation Turks still don't consider themselves German, then someone with black skin adopted as a child might consider themself German, it's about culture not race, we're not in last century anymore. Proportion of young people with immigrant background is high in many Westeuropean countries, if they don't integrate into society they won't be willing to defend it.
You seem to exactly know what I'm babbling about. Parent commentator somehow confused "looks like" for "is citizen of", something you seem to grasp perfectly well.
For all we know, 100% of the people the parent saw were actually "Young Germans", as you cannot tell people's nationality by just looking at them. Unless of course, "Young Germans" is actually referring to something else, not people's nationality.
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.