Nevertheless, their hatred and jealousy for Jin Rou didn't diminish. In their eyes, he was greatly favored by the mortal old man here.
First, the old man acted as the overseer of the bet and made Abyss Scion pay for it forcefully due to reneging, with an interest at that.
Second, he spoke for Jin Rou regarding the matter when Treemountain Ancestor appeared. It was Jin Rou's matter, to begin with. So, the interference of the mortal old man wasn't needed.
Third and last, they just spoke a bit and he was already offering the other party a free pass to Dragon Sky? If he could do it, why couldn't he give them free passes, too?
The mortal old man had a few clues regarding Jin Rou as he observed him carefully. But, with no confirmation, he couldn't say who was this ancient existence. Remember, he even knew the long ago Pandemonium Incident and the existence of Dragon Emperors.