This isn’t free. It’s a loan. The goal is that in decades from now when you’ve succeeded, you repay the loan. If you don’t and default, you owe something to China.

That's certainly one way to frame it.
Another way would be selling oversized infrastructure projects t developing nations, financed by predatory loans backed by a country's natural resources.
Also the work itself is performed by Chinese companies, so unlike regular domestic infrastructure projects, it doesn't even benefit the local construction industry.

China is effectively subsidizing its own industry with other nations' money.
And if the project fails to deliver the "optimistic" expectations. China has more or less free access to natural resources without having to stage an invasion.