You might be correct from a grammatical standpoint, but that is not how the term is used in the English language. Of course in Spanish, Portuguese and other languages it is a different context. I remember learning this distinction back in high school Spanish. In American English you would typically be referred to as South American. English typically distinguishes between the North, South and Central Americas. Amerigo Vespucci? True, but there is only one united States of America. On a related note, try calling a Canadian an American and see what reaction you might get. If you want to be pedantic, Columbia usurped its name from the U.S.A.