I know, I'm one of them. Nonetheless, it still exists.

> Revoking someone’s citizenship is hugely controversial. The Universal Declaration of Human Rights enshrines having a nationality as a right, forbidding countries to arbitrarily deprive someone of it.

It seems to me that if I were an EU citizen, the EU would be the ones who had to remove my citizenship, and that would be a very controversial step. I don't recall long winded speeches in the UN denouncing the EU for forcefully removing the citizenship of millions of people, which leads me to think that it's not a "real" citizenship.

The UDHR, Article 15, says that everybody has a right to have nationality and can't arbitrarily be deprived of nationality. The EU is not a nation and nobody has an "EU nationality", so depriving somebody of their EU citizenship doesn't violate Article 15. People in the UK retained their nationalities.

"German citizen" == "Germany nationality"

"Nigeria citizen" == "Nigerian nationality"

"EU citizen" != "EU nationality"

Sounds like you figured it out. Germany and Nigeria are nations, the EU is not. Appropriately, Germany and Nigeria are represented in the United Nations, while the EU is not.