I wonder if he is also getting confused about what 'diffusion' is. He thinks a photon of light hits the wall and then gets 'spread' when it bounces off but that single photon still bounces off in one direction and stays the same brightness (ignoring particles in the air etc), just that as the wall is not a perfect mirror it does not bounce off at the same angle as it hit. However other photons that hit the wall at an angle that would not bounce towards his eye in a mirror, will bounce towards his eye because the wall is uneven so the wall looks uniformly lit rather than just showing a reflection of the light source in one place (assuming we are not using very shiny paint)
Inverse square law does not apply to photons; otherwise a candle would be invisible if you were more than a few feet away, hell everything would be invisible!
The falling off of light over (large) distances is diffusion and diffraction due to dust & water etc. in the atmosphere.