El Salvador is just taking advantage of certain conditions in the loan agreement that were ambiguous or perhaps flexible. Somehow, the country is able to skirt the condition that prohibited its public sector to further purchase Bitcoin.
As I'm interested how exactly El Salvador does this, I googled around a bit (AIs weren't helpful in this case).
I found
this Spanish article which lists several ways the government can buy Bitcoin without using taxpayers' money, citing an
X thread by "Bitcoin Beach":
1) Transaction fees and "donations" which could go to the Bitcoin Office. I guess they refer to fees in Chivo (the article unfortunately isn't that clear here, and the X thread also doesn't help, instead confusing me more - it mentions help by the US government ...).
2) Mining. The government could support private mining facilities in the country, which as a compensation would return Bitcoins to the Bukele government. Unfortunately the article is also not detailed here, but I guess this "support" could be done for example with tax exemptions.
3) Adquisitions by the private sector. This would be a similar "loop", e.g. the government "supporting" companies (e.g. via tax exemptions) and these companies also would transfer the coins to the government's or the Bitcoin Office's wallets.
If I were to summarize what I've read, it all boils down to the National Bitcoin Office (ONBTC) not falling within the bounds of the fiscal sector. Its activities are considered non-fiscal. It operates with a certain level of independence or autonomy which makes it exempted from direct fiscal oversight. ONBTC's legal and financial structures are designed in such a way that its Bitcoin purchases are done outside the country's fiscal accounts.
Yeah, being non-fiscal, the ONBTC has a non-budgetary funding. However, it has various sources of funds including the private sector and external investments, except the national budget. However, it's also possible the body still uses public funds for its purchases, albeit classified as investment. Meaning, they're still outside the fiscal boundaries. As in other countries, public investment funds are separate from fiscal accounts.
Also, I think the IMF is actually being lenient with El Salvador. As mentioned in the news, they're focusing heavily on other more important fiscal aspects.