It may not beggar quite as much belief as you think. I don't know what the US legislation says but here it says this about a face covering:
//“face covering” means a covering of any type which covers a person’s nose and mouth;//
And that's it. It does not say it has to be of any particular cloth, or that it must be capable of capturing particles of any particular size. It must cover the nose and mouth. Miss Del Ray's face mask seems to achieve that.