It's the specific country being referenced, I think.

They wrote that they were talking about country code TLDs vs not, not about US vs. other countries. (Which is what I would've said too, it's a more general point than thinking about anything specific to one country.)

Ironically that one country happens to be the one that also controls gTLDs like .com, as others have pointed out, so arguably .us is the one ccTLD that isn't any more or less likely to be reliable.