the man described half of Triffin’s Dilemma
When your currency is the world’s reserve currency (or the major one), foreigners will want, and need, your currency, to do business and transact in the world. Not only with America itself, but among each other. When China buys oil from Saudi Arabia, they still (mostly) do that transaction in US dollars
It builds up a huge demand for US dollars, and assets denominated in US dollars.
So the USA must supply the world with dollars. How? By trade
But as mentioned, it’s a dilemma, or paradox. The USA can’t infinitely supply dollars to the world - at some point we devalue the dollar and/or ship our entire manufacturing base to the rest of the world. And then the game ends.