Most of those jobs are not coming back, unfortunately. The job market is shifting.
That doesn't address Buckeye's point, which I think is a good one.
You are correct, my apologies. I just do not see how it could be that offensive. But I will stick to the term Midwest.
Think of it this way. People embrace the term "blue collar." It gives them a sense of pride. "Non-college-educated white," on the other hand? You are, effectively, just calling people dumb.
As has been pointed out, the Midwest and the Rust Belt are not entirely the same--Rust Belt equates more with the Great Lakes Region, but that's not really my point either. Let's look at Ohio, for a minute. Columbus falls outside the rust belt, due to it's government-health-education economy, and so people there don't care so much. But look at Youngstown. Look at Cleveland. Look at Lorain. (And Pittsburgh, and Detroit, and Gary, etc.) Yes, these areas are going through a rough patch, but when you tell people they live in the "rust belt," you're seeing the forest and not the trees. You're telling people they live in a sh**t hole, and that's going to offend people who love their cities, both in sickness and in health.
EDIT: As for what to call it? That's not an easy answer. I didn't mean to personally call you out, but it's rhetoric both parties -- the Democratic one specifically -- need to seriously reconsider.