$7k is a year worth of wages for your median Chinese, equivalent to roughly $25k in the US.
Also good luck leaving any country if proceedings have been started against you because of unpaid debt.
It needs to be raised by the opposing party in US courts, then the judge will consider flight risk and confiscate their passport if deemed necessary.
Does this happen in the US? I have heard tons of stories of people in tens or hundred of thousands of dollars in debt (other than usual mortgage and car), but loosing their passport is never part of the story.