You can be technically a citizen, but unable to prove that due to administrative errors or your parents bullshit. One weird case I remember from the news was people believing in the "sovereign citizens" thing and not exchanging their ussr passports to Ukrainian passport, than having a child and either not registering their birth or doing something of that kind.
As a result the parents can get citizenship, but don't want to, as authorities don't bother them much, but their now adult child is technically a citizen, but doesn't have paperwork to prove their status.