That may be the case though I don't recall any statutory definition showing American citizen (U.S. citizen or citizen of the United States) to include U.S. nationals (but it could). The key distinction worth noting, IMHO, is whether or not one regarded to be a citizen of the United States is in fact a "person born subject to the jurisdiction of the United States".
P.S. Florida government officials are on record referring to Florida as a nation.