The article reports that Bukele claims 2.1M active users. Setting up a lightning channel still requires a transaction. It would take days (even weeks maybe?) for Bitcoin to handle 2.1M such transactions even if it did nothing else, and an enormous amount of fees.
More likely, the Chivo app is just a centralized system like a bank (i.e. a database tracking everybody's transactions and balance) and it only interacts with certain entities outside of the Chivo system via lightning.
More likely, the Chivo app is just a centralized system like a bank (i.e. a database tracking everybody's transactions and balance) and it only interacts with certain entities outside of the Chivo system via lightning.