You’re not really making sense. “A debt paid,… is still a debt that has to be paid”? If the debt is paid, it’s already been paid.
Assuming Afghanistan owes China for the infrastructure, then that debt would be paid by giving them copper. Bought and paid for. So how are they saddled with debt? Where’s the trap?
Obviously the deal will be a lot more complex, it might not be a great deal long term in some respects and I’m sure there’ll be a measure of corruption (there almost always is, everywhere), but at the end of the day Afghanistan is getting infrastructure it couldn’t build on its own and China is getting resources it otherwise wouldn’t have access to.