I always thought of it as, NYC being the starting point for the vast majority of Jews in America (as in the Ellis Island days) so anything “away” from the starting point is “out” of the town.
Today, since many jews (though I doubt as many as NYC) start out in places West of the Hudson, I suppose there is no longer an “in” or “out” when it comes to towns.
Unless we’re talking mindset, and then, I agree with GAW.
If you’re not from NYC, you’ll never understand.