As far as I can tell, they think the dollar should have been falling all along, due to the central bank pumping the money supply, and that it's really just inertia keeping it up. The vaccine jump-starts the world economy, and the US loses out if it keeps artificially stimulating its economy.
That said, it should have been doing that before the virus, and it should have been doing that during the lockdowns. So they're really just saying "We have no idea why quantitative easing hasn't already ruined the US economy, but maybe this will make people return to their senses." (I also have no idea why so much quantiative easing hasn't crashed the dolllar, except to guess that everybody else somehow has it even worse.)
