Yeah, if it's a small country with few citizens but notice that they are still using their fiat, it's because they still can't fully let go of their fiat system. It's because it should not be replaced. Many bitcoin believers want to fully replace the fiat system and make bitcoin the only currency we will use, but the thing is, I don't think that is practical and should be done. I have been a bitcoin fan ever since, but I don't agree that bitcoin will replace all fiat or banking systems. What I want is that bitcoin will be legalised and will be regulated worldwide, but still, there's still a fiatsystems. What I want is that bitcoin will be legalized and will be regulated worldwide, but still, there's still a fiat system. Let's take, for example, El Salvador. The country is accepting and adopting bitcoin, but they are still using fiat because they are not yet ready for that.
As far as I know, El Salvador does not have its own fiat, but rather uses the US dollar. This was before Bitcoin was officially adopted to become the main currency in El Salvador.
I do not know if the fiat you saw is the US dollar, but in any case, given the difficulty of using Bitcoin for small, quick daily payments, there must be another currency besides Bitcoin in El Salvador, which is most likely the US dollar, because El Salvador does not have its own national fiat.