That was very perceptive. That would get him out of the implication that there might be a God that we owe. He was very honest, though. He wasn't taking the easy way out. Guilt really means more than what we owe ourselves.
Debt is a personal kind of thing.
That bring us to the question of God. If we have this moral law it implies that there is someone out there that put that moral law in us that defines the moral law because laws are something very specific. They aren't the kinds of things that happen by chance. But we don't just owe in some kind of generalized sense, we owe somebody. We don't owe the law, we owe the person behind the law.