Yet it is not. The purpose of a muzzle is to prevent a dog from barking and biting. The face mask which you call a muzzle is designed to stop spread of liquid particles. I am not in favour of face masks, I do not like them. But it sounds stupid to say muzzle. All i think of when I see it is a boomer saying demonrat instead of democrat.Things are named after their purpose. It's a "face mask" to muzzle humans, like we muzzle dogs.
You could argue that the purpose is to keep the idea of the virus constantly at the front of people's minds. Without the face masks most people would more or less forget there is a "pandemic".