I learned the other day that “upstate” is a specific region of New York State and not just “all of New York State that isn’t the city” but I think that’s lame and am gonna force the term definition change. If it’s not the city it’s upstate
the enemy's state is up
Honestly whoever told you that is stretching the truth, and maybe is just wrong. In practice anyone in NYC will refer to any part of NYC that isn't NYC or Long Island as upstate. "Oh you are from New York? NYC or upstate?" I don't think people debating "does Yonkers count as NYC?" really changes that.
Every state has an upstate. New Yorkers are just being obnoxious by pretending theirs is the only one. When someone says they're from "upstate," unspecified, you should say "so like Orlando? Tallahassee?"