Looking at the whole article, the author is making the argument that the Chinese do not "invest" for monetary gain or loss, but rather use the Treasury purchases as a way to decrease their supply of dollars (a strategy necessary to keep their currency devalued, worth less than it would be if it were fairly traded without central bank intervention).
While it certainly is correct that a debtor at risk would have some concern for default, the point of the article is that (the author asserts) China doesn't particularly care for the stream of interest payments on it's bonds, or even the principal payment back at maturity, but rather the tool that the "investment vehicle" (Treasury) provides, it is China's most powerful weapon in sustaining its relatively devalued currency.
While it certainly is correct that a debtor at risk would have some concern for default, the point of the article is that (the author asserts) China doesn't particularly care for the stream of interest payments on it's bonds, or even the principal payment back at maturity, but rather the tool that the "investment vehicle" (Treasury) provides, it is China's most powerful weapon in sustaining its relatively devalued currency.