I'm a native English speaker, and I also had a hard time finding the lie. Especially when the context shows that masks were not "not recommended" due to potential lack of efficacy, but due to shortages.

Clearly if they were being recommended to front line workers, etc, they are expected to have at least some efficacy.

Personally, I think it's a bad example of "experts lieing", even if it is potentially a lie under some very narrow reading.