I think you're conflating the idea that a reserve currency needs to be the same currency that a person interacts with on a daily basis.
Commercial trade and government debt operate a such large quantities, that they are essentially a market unto themselves.
This is essentially how gold worked wrt the gold standard, except that with gold, a large find in one country increases the wealth of that country, or makes it subject to war, as other countries want to capture that value for themselves.