[citation needed]
Oct 2015 - Oct 2016 they've reduced their total holdings by ~139 billion. This could have been through either outright selling, or just letting them mature and not reinvesting, or some combination.
Either way that doesn't really look like dumping and is practically pocket change in the scheme of US debt.
That hardly constitutes "dumping hundreds of billions of usa bonds". The net change in foreign ownership over the past year was only ($60BB).