@Dikus
The word demon god most likely refers to someone who is naturally talented in the way of martial arts (or a certain type of ki or are direct descendants of a clan/cultivation (I assume)
As for Noh, it is most likely that he severely injured the Demon God (or who knows killed him from the way they are speaking) (and he is the blond crazy hobo), and yes they are wondering who defeated him at first they assume it was the sword king but it is revealed that it is unlikely that he did since his ki is of the same attribute.
As for the painful blue lights coming out of Noh, it is most likely that he has finally opened his meridians which are the central pathways for ki and or he has ascended to another realm in cultivation this novel assumes that you are knowledgeable about wuxia (cultivators and ki) which is what makes it so immersing. Him coughing up blood is from his meridians forcefully being opened. This can be seen in the previous chapters as his back bulges and such.
I hope this explains a little bit at this point we will most likely learn more as the story progresses or at least I hope we do!