That is the writer giving a false impression, here is the actual quote, it is about what happens if NATO is attacked.
““If he keeps going and then he attacks a NATO Ally — well, we’ve committed as a NATO member that we’d defend every inch of NATO territory — then we’ll have something that we don’t seek and that we don’t have today: American troops fighting Russian troops.”
He repeated, “American troops fighting Russian troops if he moves into other parts of NATO.””
Biden assures Zelenskiy that NATO membership in Ukraine's hands, Kyiv says December 10, 2021