Among native English speakers, “American” almost always means someone from the United States. That’s partly because, unlike every other country, the US doesn’t have a convenient adjective for its residents.

However, after a few years in Central America I’ve broken myself of this usage. Spanish has an adjective for US people (aside from gringo, etc.) that I can use in Spanish, and when speaking English I find some other phrase. Note also that for many people in South and Central America “America” is what US people call “the Americas”: one continent, not three.