A simple google search goes a long way guys. Not just insulting nationality and practically ignoring the entire statement made.
"They" historically is a word that can refer to either a single subject, or multiple. Both usages of the word in English (I have to emphasize this as the original Scandinavian word was just used as a masculine plural pronoun) developed at the same time as "þei" (literally pronounced like "they").
Ain't even an American thing, it's literally just always been used like this since it's conception.