OK, stop it. This is not even remotely true.
The smell of farts comes from sulfide molecules. The smallest of these, hydrogen sulfide, is two hydrogen atoms and a sulfur atom. No air filter can stop a molecule that small. Only an airtight barrier could stop a fart.
A virus molecule is several orders of magnitude larger than the sulfides and thiols that constitute the smelly part of a fart, especially a virus that has a lipid (complex carbon) outer layer like coronavirus does. Coronavirus molecules are, relatively speaking, HUGE.
So say what you will about whether or not these viruses can be stopped with a mask, in or out, but this argument that "it can't stop a fart" is so grossly unscientific that it must have come from some overseas Facebook troll farm.
If that coronavirus molecule is "huge", keep in mind the pores in an N-95 mask are even larger.
(I have worn respirators that will stop the smell of a fart. They have a limited ability to capture H2S with the right filters. They are not certified as either escape or entry equipment for even STEL/TLV environments, but it is a feature that comes with the acid gas filters. They are a quantum leap above what is being touted as "safe".)
That doesn't even go into portable air filtration units used to provide positive pressure environments, nor SCBA, nor piped in air in full suits, which would be more compliant with BSL-4 protocols.
What is being bandied about as 'safe' is really on the low end of the protective spectrum.