El Salvador probably wanted to keep their image as a bitcoin friendly country. Not only do they want to appear friendly to bitcoin, it seems like they want to be a country known for having a lot of bitcoin and possibly get investors in their country. I have seen some people doubt IMF's reports but what do you think? It makes sense if bitcoin has become El Salvador's political move.
If you want to make progress as a country, always do the opposite of whatever IMF says just like China did and became a super power. IMF was not created to help any nation develop but to keep them in perpetual slavery. If they help you by given you loan, open the book and look deeper and see that they are actually killing you. It was IMF that advised the new president of my country to devalue our currency, remove energy subsidy and that eventually collapsed our economy and send people to abject poverty because we are a net importing nation and depend on the dollar for everything. People are struggling to even feed because the prices of basic commodities went x5. Even if El Salvador did not purchase a single Bitcoin but claim that they did, the moment IMF countered them that they did not buy, I will believe El Salvador.