Because someone is a President doesn't make what they say insightful or truthful.

A government could print money instead of collecting taxes but the resulting price inflation will adversely affect lower and middle income wage earners most (than high wage earners) since they spend the majority of their earnings on the consumption of goods and services.

But if the El Savador President thinks that Bitcoin is scarce...he is wrong! The protocol could be changed to increase the amount of Bitcoin. Typically these are known as "forks" where other digital "currencies" are spun off from Bitcoin to magically create other digital currencies.