Westchester is absolutely upstate NY. And while no one from Buffalo considers Buffalo to be "upstate NY" (it's WNY) and actually refers to upstate NY as "downstate," pretty much everyone else in the world considers any part of NY outside of the city that is not on Long Island to be "upstate."
My point isn't distance, but rather regional identification. Westchester Co is certainly upstate NY, and most of the world thinks Buffalo is in upstate NY, (except people from Buffalo).