Well, it's fun to stand and point at the insularity, of course, but I'm more interested in the way language is working here. I'm assuming (perhaps rashly) that whoever wrote that sentence doesn't actually believe that the maid Flora is American. In that case, the obvious inference is that the individual semantic components of the phrase "African American" have become fused into one, purely racial epithet, the "American" functioning semantically as "person originating from place that I just mentioned". But does this happen with any of the other double-barrelled epithets in common use? Do Italians in Italy ever get referred to as Italian Americans? Or Chinese people from China as Chinese Americans? I don't think so - at least I've not seen it. It seems something else is going on, then.
Another comparison might be with the way Americans talk about white people as Caucasian (where did that come from, by the way?) without implying that they're from the Caucasus - unless of course they're Dzhokhar Tsarnaev. But my impression is that "Caucasian" is used as a semi-technical word - I've mostly heard it in police descriptions - not in ordinary conversation.
Looking closer to home, a comparison might be with English people saying "English" when they mean "British" - which is of course a reflection of English dominance of the Union and the privilege-cum-complacency that that engenders. Perhaps we can extrapolate something similar for "African American", re. American dominance of the entire planet? But that still doesn't explain why this usage is restricted to people of African origin. For a while I wondered whether it might have something to do with the fact that Africa is a continent rather than a country - but then, Asians don't tend to get called Asian Americans, do they?
I still don't have a satisfactory answer to this. Thoughts?