To conclude what the senior had said, the world behind the door was just a nightmare formed by Men Nan's main persona. When the boy woke up, the door connecting the real world and the dream would close, and they would be trapped in the dream forever.
Chen Ge would have believed the old man if not for the 'door' that also appeared at the Haunted House. The appearance of the 'door' at two different places was not something that can be explained by a boy's nightmare. Chen Ge did not reveal that fact. He looked at the senior and asked another question. "You said that this is the boy's nightmare and everything here is a reflection of the boy's subconscious. Then can you tell me, what role do you play in this nightmare? Or rather, what does you being in his nightmare represent?"