When I moved to France for grad school a few years ago, people would sometimes ask me if I was English, which I found a bit insulting. I already spoke French and even though it had been several years since my study abroad in France, I was able to “me débrouiller” soon after moving. I’m not sure why some people thought I was English, since my accent when I speak French does not sound English (at least not to my ears). After I’d been in France for about a year, my accent would prompt the question - “Vous venez des Antilles?” Umm, getting closer but no.
Other guesses have included The Netherlands, Mexico and the most recent was Morocco. This was from a cab driver who said I had a slight accent he couldn’t place. Inevitably, when I tell French people that I’m American they want to know where I learned to speak French and they’re surprised that I speak French so well (i.e. I can say more than bonjour and merci). I know that Americans don’t have a reputation for being able to speak anything other than US English (and some can barely handle that), but is it really so surprising that a number of us are able to communicate in another language? I doubt I’ll ever lose my accent, so I’ll just continue responding “J’suis américaine” or “Je viens des États-Unis” and hope people won't always ask for the history of my language education.