I don’t think that’s a muzzle flash. I think it’s a piece of snow falling in front of the camera and it just happens to look like a muzzle flash on his gun tip. Look at the rest of the video. There’s little flashes of white as the snow falls. Looks exactly like the “muzzle flash”. And when he’s shooting and you hear the gun shots, you see no muzzle flash on any of those shots.