But anyway, a large debt holder can bind up the borrower by announcing they think the debt they hold is worthless. The impact would depend on how much debt it was, with a large amount being dumped almost certainly increasing the cost of borrowing.
If I go to a bank, and I get a loan, then the terms of that loan allow the bank to do that.
If I sell a bond, then I set the terms, and I say that you can’t do that. You buy the bond understanding the terms.
China owns treasury bonds, they don’t have the ability to “bind up the borrower”. They can sell their bonds at market prices, but they can’t say “this debt is worthless, pay us now”. That’s not how bonds work.