I don’t think it’s a lie at all (at least not in the English language meaning of lie). There’s no good scientific evidence which supports wearing a mask when you’re just out and about as having any benefit in protecting you. There’s none in Asia either. And it’s not like people haven’t studied it. They have, a lot. It’s just a cultural thing, like “fan death” in South Korea - they can find professors who claim that’s a real thing and put them on TV, but it’s a ridiculous urban myth.
This is obviously less ridiculous, and if you’re going to be in close proximity or sustained contacted with infected people, masks do offer a modicum of protection, which is part of why healthcare people wear them. Though as Ed notes, basic surgical masks may offer little protection here. N95 masks seem to be more useful. You’d think they might benefit people shoving in to trains and stuff, but AFAIK the rates of stuff like flu are the same in mask-wearing nations as non-mask-wearing ones (Bill speculates this is partly because people used to masks are incautious when unmasked and behave worse about coughing/sneezing, but I don’t think anyone actually knows why).
However, masks do protect other people, and at this point, an awful lot of people out there are walking around infected but either asymptomatic, or with mild symptoms, or even non-mild symptoms. So it makes sense for them to ask people generally to wear masks, because then you potentially get more infected people wearing masks.
Another example of irrational-seeming behaviour is China (and other countries) using vast amounts of supposedly anti-viral (but that’s questionable) “disinfectant” to hose down entire cities. There is, as far as I know, not even a shred of evidence to suggest this does a damn thing. Nor would it make much scientific sense for it to. But significant resources are expended on it. It’s one thing to spray specific indoor or confined areas where infected people have been for some time, and other people will be going, but streets and stuff? Um. Not really.