I don't think they ever use the term "metahuman" anywhere in the Marvel Cinematic Universe -- that's a DC term. In the MCU, they have used the term enhanced" people, to describe superheros like the Avengers. For example, that is the term used in the Sokovia Accords, which Iron Man (but, possibly, not Tony Stark) falls under.
In this case, Tony would be considered "enhanced" only in the sense that he can pilot a special enhancement suit; James Rhodes and Sam Wilson (Falcon) are in the same category. As far as Tony's suits go, we've been told that they are keyed to him, specifically so the government can't steal them, so in his case it makes sense to consider him enhanced. It's not as clear how, for example, the Iron Patriot suit vs. James Rhodes as a person are listed under the Accords.
Note that Tony Stark, without the suit, is still a member of the Avengers; this means he falls under the Accords as long as he wants to continue in that role, because they also govern the Avengers behavior as a group. That's independent of him being "enhanced", though.
In addition to that, "being wealthy" isn't Tony's "superpower"; they don't play this up quite as much in the movies, but the idea is that Tony is a genius. He's generally considered the greatest engineer in the Marvel universe, ranked up with people like Reed Richards (not in the MCU, obviously), Hank Pym, and Bruce Banner as one of the smartest human beings alive. His wealth is a consequence of his genius.