Maybe you can play a game under protest and file an appeal later. But in this case I haven’t seen any indication that the player did that. Deciding two days later to protest doesn’t seem right. I see no compelling reason to overturn the basic rule that resignation (or mate) ends the game. Unless evidence is presented showing there was an agreement to a draw, which ended the game before the resignation, I don’t see sound grounds for an appeal. In my mind, the fact that the player immediately said “no draw” strongly suggests there was no meeting of the minds.
If any of my tournaments are done without myself at the tournament: then take me behind the building and have me “SHOT”.