After finishing the conversation with Yu'er, enter this house and speak with the madman again.
This time, his mental state has returned to normal when speaking with him. After triggering this dialogue, interact with a grave mound later in the main storyline to obtain an accessory.
Let's head back to the village entrance and find the person sitting on the carriage.
Speaking with him will grant you the book [Clues to Jianghu Mysteries #2: Order for the Adjutant].
