>I have no idea where it came from or why.
It was very likely a product of the Reformation, and almost certainly had nothing to do with debt. Specifically, the ethic arose from the philosophies of Luther and Calvin in the 16th century. Prior to L&C, the dominant Catholic line held that hard work was a means to achieve salvation. Work was punishment. If you weren't performing good works you would go to hell. Working hard to serve your god? Good: perhaps you will be saved. But don't work too hard, because hoarding wealth is a sin. Pay your excess forward to the Church and it will help your cause in the end.
Luther didn't exactly turn this conception on its head but altered it, which opened the doors for later change. He believed that work was good because it served not only the individual but also the social whole. The main expression of this was a dissolution of occupation-based social hierarchies. For example Luther rejected that something like agricultural work was inherently less valuable than a monastic calling. All work had value, and all work had equal value in the eyes of God. The main thing is that each person was called to work by God, and to work was to exercise your noble calling. This is basically an inversion of the concept of work as punishment.
Calvin both carried Luther further and branched out. His was probably the first interpretation of Christianity to state that maximizing profit from one's work was not only good but also required. This wasn't a call to maximize profit in pursuit of an easy life, since even rich folk had a duty to perform hard work. Rather the duty was to improve the Kingdom of God (and one's society) through investment. This doesn't mean philanthropy or giving to the poor, rather something like modern capitalism where an individual's investment (sometimes, often) produces positive effects for those around him. Devoted, hard workers help to maintain a cohesive social whole, which in turn mitigates the chaos and disorder that might stem from idleness.
Underlying Luther's and to a greater extent Calvin's philosophies is the notion of predestination. Dominant Catholic thought posited that people were born sinners but could earn salvation over a lifetime. Predestination rejected this, stating instead that God chooses the saved at birth. That is, you're either saved or you're not out of the womb, and there's nothing you can do about it. During your life, you can't know whether or not you are one of the elect. However you sure as heck want to be, so you do your best to live in the way you think the elect would live. If you succeeded, this could be perceived as evidence of your having been chosen to be saved. Hence the social drive to work extremely hard and produce as much as possible.
The above is probably a bit rambling and somewhat of a bastardization, but it's generally correct. Given that, I'm not surprised that in a historically Catholic region you came across a very Catholic take on work, which is at odds with the conception of work you're used to in historically Protestant America.