I don't see where the relevant information is on that page. It has the US's total debt to GDP ratio at 122%. Public debt is a subset of that so it has to be less than 122%.

I see what you're saying though, on the debtclock site, a bunch of countries have higher foreign debt than public.

Here's a source for "public debt" and "external debt":

Public debt, sometimes also referred to as government debt, represents the total outstanding debt (bonds and other securities) of a country’s government. It is often expressed as a ratio of Gross Domestic Product (GDP). Public debt can be raised both externally and internally, where external debt is the debt owed to lenders outside the country and internal debt represents the government’s obligations to domestic lenders