That's the US way of seeing it, not the UK. They're Nigerians. Them simply being born here is not good enough, they have to have families with a legacy of being here for a few generations.
I'll use a Polish analogy,
Polish people live and work in the UK, however if the couple has a child here, the couple from Poland will consider them Polish, not British, even though they were born in this country, the same would apply to me if I lived in their country.