Exactly. She's black, wearing tribal-esque outfit and is called Ngozi. It is 100% acceptable and understandable to ask where in Africa she was from. It's taking an interest in people and their heritage and making conversation. Historically engaging in conversation with someone and asking them about themselves or their history was seen as taking an interest, compassionate and engaging.
I've travelled all over Africa for business and pleasure. I've got family and personal interests in its geography, people and history. This is going to make meeting small talk and just general conversations with people really very awkward. One of the most interesting nights I've ever had was a late night curry at a table set up in the middle of the pitch at the Mombasa Polo Club with various East Africans (Black, Indian and White) all chatting about our various heritages, religions, differences, similarities etc. It was eye-opening and wouldn't have been half as interesting if I didn't ask questions.
Jeez, I was in Heathrow a few months ago, a woman in a shop that was serving me had Tanzanian flag pin. I noticed, asked her if that was where she was from and blasted her with some very rudimentary Swahili. She was happy, I was happy, it was a fun little interaction.
It's a posho/establishment witch hunt and a way for Ngozi to get her 5 minutes of fame.