OP, I am with you.
SH and NF both seem (I don't know them personally) to be competent adults.
SH has chosen to apologise, NF has chosen to accept the apology.
From what I remember NF said from the start she didn't want a witch hunt, but wanted people to educate themselves on the impact of this sort of behaviour. Being asked the same question over and over again, rather than accept the answer is rude, and in the context implies that the original answer wasn't believable because NF is black.
On the other hand, I am interested in people's heritage and culture, and if they are happy to talk about it I an interested in hearing about it. It is possible that this is what SH was asking, but in the wrong way and not accepting that NF had no obligation to talk about it.
Intention does not equal impact, but I think intention is relevant in admitting a mistake, apologising, and doing better in future.
In being interested in other peoples experiences and heritage I do not want to imply that - if they are not white British for generations - they do not belong here. DD is black African (from South Africa) and we talk about her birth heritage as well as her heritage by adoption. I would be furious if someone said she cannot be British because she is also black and African by birth. But it can be a fine line between showing interest in someone else's heritage and implying that they do not belong. I can imagine a situation where I get it wrong, and would want to apologise - without any pressure on the person I had hurt to accept the apology. The alternative is to block any conversation about different experiences and heritages, which I think would continue to privilege the white British heritage.
DD also sometimes wears clothes that reflect the traditional clothing of her birth heritage for special occasions - why shouldn't she? And for day to day wear she generally wears jeans/trackie bottoms and a T shirt. Why shouldn't she? They don't invalidate each other. I wear jeans/trackie bottoms and a T shirt most of the time, and occasionally put on a nice dress and wear heels. That doesn't mean I am being inauthentic when I wear the dress, or when I wear the jeans - just that I dress differently for different occasions.
So, you can read whatever you want into this story.
Personally I think there is a case to be made that SH did not realise the impact of her words and actions at the time, and once she found out she wanted to apologise. And that NF was able to recognise that SH's words and actions came from a place of ignorance, and therefore was willing to accept the apology.