Shuhang had cured infections related to the evil energy of the Netherworld when he had been acting as a genius doctor in the Beast Realm. It was during that period of time that he'd collected most of the materials he needed for the Thirty-Three Divine Beasts' Combined Magical Treasure.
Therefore, when the lady in the long skirt asked about this, Song Shuhang immediately connected them to practitioners of the Beast Realm.
As he was in a transparent state due to the small black room, with the Beast Realm also being a part of the universe, the people there should have forgotten about him.
However, although they couldn't remember Tyrannical Song's appearance... The incident of the Beast Realm having a lot of its dwellers infected by the evil energy of the Netherworld was already big news, so the people of the Beast Realm would naturally not forget about his actions related to this.