First off, no, they aren't:

http://ticdata.treasury.gov/Publish/mfh.txt

Second: how, exactly, would that work? For the millionth time you cannot sell without a buyer. So if China is "dumping", someone else is buying. Or do you think they're just lighting these bonds on fire? Guess who wins in that scenario. Hint: not China.

You know, there's so much controversy about "fake news" lately, but the reality is that people will seek out the stories that fit their narrative, rather than looking at the data. Nobody to blame but ourselves.