(I'm not sure if your comment was genuinely asking about the number of political parties in the U.S., or sarcastically remarking on the fact that there's only effectively two parties)
While there are technically more than two political parties, the vast majority of Americans support one of the two major parties - the GOP (a.k.a. Republicans), and the Democrats. Between them, these parties more-or-less represent most of the range of political discussion and ideology in the U.S. The next-largest party is generally considered to be the Libertarians.
Thus, while the statement "Americans from both political parties" may contain a technical inaccuracy, as there are technically more than two parties, it's a useful shorthand for "Typical Americans, regardless of political affiliation"
As for why there's only two major political parties in the U.S., it's likely the result of most elections being simple plurality (a.k.a. first-past-the-post). This heavily encourages potential candidates to compromise and coalesce until there's only two candidates, to avoid the spoiler effect.
While there are technically more than two political parties, the vast majority of Americans support one of the two major parties - the GOP (a.k.a. Republicans), and the Democrats. Between them, these parties more-or-less represent most of the range of political discussion and ideology in the U.S. The next-largest party is generally considered to be the Libertarians.
Thus, while the statement "Americans from both political parties" may contain a technical inaccuracy, as there are technically more than two parties, it's a useful shorthand for "Typical Americans, regardless of political affiliation"
As for why there's only two major political parties in the U.S., it's likely the result of most elections being simple plurality (a.k.a. first-past-the-post). This heavily encourages potential candidates to compromise and coalesce until there's only two candidates, to avoid the spoiler effect.