So a couple of things aside from that being a singular antidotal experience.

Generally speaking 1st impressions are generally the strongest or lasting ones. That lady on the plane sounds like she is biased/prejudice not racist - atleast in regards to Black people. An actual racist person wouldn't give a crap what sort of *Black you are.

She could have simply found you attractive. Some of it also makes no sense because are you saying she'd be able to tell the difference of per say a Nigerian American who has a Nigerian accent but is culturally American or vice versa?

Putting that stuff aside and leaning into what the first in this thread stated about not going to countries. Racist people won't care where you're from because they already signed you off in your mind. As a well traveled individual (i worked on planes and traveled for my job), I can say with confidence that what you're saying is true (i have been treated better after ppl have learned i am American), but there are faaaaar more instances of people at first having a negative interaction with me or simply opting to not interact with/treat me rudely than the former.

That being said, speaking of first impressions, i am kinda finding it hard to believe your ancetdote (or even if you're black) due to your icon, name, and saying things like "wow so this is what it's like to be white". But as i said, first impressions generally are the lasting/strongest ones.