Or maybe it was used all along and we just didn't hear it. Like "Federation." The term was never used until "Arena," with "United Federation of Planets" not established until "A Taste of Armageddon," but we retroactively assume the name was in use all along. Fictional universes retroactively expand their worldbuilding all the time. It doesn't mean the thing didn't exist before, just that the writers hadn't yet thought to establish that it did.
Yeah, that's possible as well. I was just noting that maybe it was a term that Dr. Soong created for his new band of merry supermen and the term stuck. But sure, it could have been a term used previous to that as well.