This is what I’m inferring:
The blonde hobo is the Metal Demon God; the one Noh’s Master did not want Noh to ever run into or become like. A few chapters back when the Demon God was brought up, there was a picture of 2 Asura Demons, one depicting Noh’s Master, the other for the Blonde Hobo (Demon God).
Noh won against the Demon God by using his brains to fight and win. However he was unable to truly finish the Demon God as he lost consciousness. While unconscious his Master reprimanded Noh for losing to that lump of flesh, or feeling even pain from it. To his master’s eyes the Demon God is probably powerful, but Noh’s training should be more than enough to compensate for it. It probably could be if he still had the picture book for his training.
Cue Noh waking up and his meridian/pressure points going off. I believe the bath his master made him take was a more gentle way to repair and improve his body. It could also be a way to not become that lump of flesh. The black flakes being his blood being cleansed and to help ease the pain.
Even if both are the same element there are definitely levels to strength within the elements themselves.
Where Noh is: the bodyguards for the girl, the Administrator, or a 3rd party could have Noh. I want to think it would be the bodyguards, repaying the debt of protecting the girl.
Also with respect to the image of the earth demon god I believe that to be slightly representative and a bit figurative. I also want to think when someone is called a demon god it is because they went berserk for whatever reason; failed cultivation, sadistic enjoyment of something within their martial arts, or rage.