@ramsey The UP is anything you have to go over the bridge or drive to from Wisconsin - it's physically the upper peninsula and if they actual said that, they're wrong.
However there's some weird Michigander terminology you might have misheard. Are you sure they didn't say "up north" instead?
That's a different thing. Pretty much anything north of US 10 has generally been the dividing line for "up north" in Michigan. Runs from the edge of the thumb to Ludington on the lake.