The article explains that El Salvador, like Ecuador, is fully dollarized at present. Here in Argentina only the real estate market is dollarized. However, not dollarizing your domestic economy doesn't mean you can hold your central bank's reserves in your own currency; not even the US can do that.

They need access to a USD settlement network for imports/exports.

How does BTC change that?

Very few people are willing to accept El Salvador Sovereign currency. Many people (and maybe countries) will accept BTC.

The national currency in El Salvador is the US Dollar. They retired out their own currency in the 2000s.