As someone who's very well informed on that corner of financial markets, you probably realize that China controls much more than $660 billion of US Treasury securities.

I'm sure you also realize that when a large holder sells a significant stake of any asset, traders anticipate they will sell more in the future.

Example 1: Berkshire Hathaway selling $47 million of BYD and the market price dropping 8% the next day, wiping out $10 billion of market value.

Example 2: Musk selling 0.6% of his stake in Tesla, and the market price dropping 15% the next day, wiping out $187 billion in market value.

Example 3: UK government announcing a planned sale of 0.3% of above-ground gold, and the global gold price plunging 10% before the first auction.