Answer:
Nunez was never able to convince them that he had the ability to see.
They were so much adapted to their sightlessness that they were able to do things which he could not such as hear very faith sounds, perceive the faintest odours. To compensate for their lack of sight, their other senses (touch, hearing etc) were advanced beyond Nunez's capabilities.
So even though he claimed to see, he could not demonstrate superiority over them by successfully completing their challenges. Because he couldn't convience them of his ability to see, how much more his superiority, they considerered him crazy.
In the 20th page, they attribute the cause of his "unhappiness and crazy talk" to his strange moving eyes and propose that the eye be removed by an operation.
Cheers!
