Not at all. The US dollar has the economic and military might of the world's most powerful country behind it. What exactly does bitcoin have behind it again?
This is silly. He says that IF the belief the dollar will be worthless is ubiquitous, then it will become worthless. That's a function of the market, a true fact.
The economic power and military are already calculated into that. It makes it very unlikely that people will think the US dollar will become worthless. But he wasn't talking about whether that belief is likely, but simply stating the true fact that IF everyone starts believing that, then demand crashes and supply skyrockets accordingly and it'll become worthless.
In other words, no different from any currency or any good on the market for that matter, including bitcoin.
But that's true for almost any modern currency. If everyone believed that the US dollar is worthless it would become near worthless. There will always be some demand because US citizens have to pay their taxes in US dollars but that wouldn't be enough to keep the dollar at anywhere near it's current value.