If he's riding on the roads with cars then that's actually a sensible use of a mask. Helps filter out some of the fumes and pollutants.
What a croc of shit. Wearing a mask while riding at even a moderately elevated respiratory rate restricts your breathing, causing a fuck bigger problem than the meager filtration of some 5 micron particulates. . And show me a mask that filters out carbon oxide, nitrogen oxides, sulfur dioxide, unburned hydrocarbons, etc that isn't a fucking spacesuit, lol