A virus is about 10 nm (10-8 m, or 10 millionth of a millimetre). It is indeed impossible to stop it with a house-made facial protection, or even a simple mask (FFP1). Only specific masks (FFP2 or N95) can stop them, and they are for health workers first.
However, a sputter or an aerosol are between 10 and 100 µm (10-4 to 10-5 m, or between 0,01 and 0,1 millimetre). They are caught by standard fabrics like those used in the tutorials. We are speaking of "anti-sputter protections", and not about true "masks", but they nonetheless protect from the contagion which, in public space, happens in major part through aerosols and sputters.