I have been wondering about this. I didn’t think ‘Nigerian’ was, as a blanket, an entire ethnicity? There are several as far as I’m aware but I can be quite clumsy when I phrase things so I tend not to ask.
You're right, 'Nigeria' is simply the (former colonial) name for a very large area of land.
Being ignorant myself, I did a quick shufti and found this:
Nigeria is a very ethnically diverse country with 371 ethnic groups, the largest of which are the Hausa, Yoruba and the Igbo. Nigeria has one official language which is English, as a result of the British colonial rule over the nation. Nevertheless, it is not spoken as a first language in the entire country
en.wikipedia.org
Smeg (aka Mrs 371!) is either a complete idiot or she cooked up a way to use a whole country!
If she's had her DNA tested, they would have found the markers for specific ethnic groups. Companies like Ancestry have become really good at that because of the number of African Americans seeking their family origins.
It would be correct (and much cooler!) to say 'I'm from the Hausa, Yoruba, Igbo and Kanuri people/groups/tribes'. There are quite possibly many DNA-tested African Americans rolling their eyes at her because she sounds plain ignorant with her 'I'm 43% Nigerian'!
African Americans don't generally use the former colonial name of a country to identify with, they proudly give their tribes' or people's names
The other thing I know from following many AA DNA stories is that it's rare for the DNA of an African American to come from just one modern country or area.
Fun facts about Oprah's DNA!
Kpelle people (modern day Liberia)
Bamileke people (modern day Cameroon)
Bantu-speaking people (modern day Zambia)
8% of her DNA is Native American
3% of her DNA is East Asian
When Oprah Winfrey took a DNA test for the PBS show African American Lives a few years back, she found several surprises in her DNA.
blogs.ancestry.com
Mrs 371's DNA profile is more likely to be like Oprah's but with a higher %age of European than African markers.
See also e.g. Prof Henry Gates Jnr. - Finding your Roots, very informative and moving TV programmes tracing people's African heritage. Many on YT.
(Oooops! didn't mean to write a whole thing about this! I just really love all this family history/heritage stuff!)