I'd never heard that before. I think the common usage is closer to Mao's 3 worlds model. Super powers, lesser powers, and exploited countries (though I'd change the third one to shitholes no one cares about)Japan isn't a NATO member is it? That's technically what "1st world" means. (The "Allies" side of the Cold War, "2nd world" is the Communist side, "Third World" was the uninvolved)
But for the record, it looks like Japan was always included as a first world country. Even if not in NATO, they were still aligned with us after WW2.