In the Cask of Amontillado, what part did betrayal and deception play in Fortunato's demise in regards to friendship?

While I agree that Montresor is unreliable and betrays Fortunato, there is one moment that suggests some betrayal of Fortunato towards Montresor:

I broke and reached him a flagon of De Grâve. He emptied it at a breath. His eyes flashed with a fierce light. He laughed and threw the bottle upwards with a gesticulation I did not understand.

I looked at him in surprise. He repeated the movement - a grotesque one.

"You do not comprehend ?" he said.

"Not I," I replied.

"Then you are not of the brotherhood."

"How ?"

"You are not of the masons."

"Yes, yes," I said, "yes, yes."

"You ? Impossible ! A mason ?"

"A mason," I replied.

"A sign," he said.

What happens here is that Fortunato has made a sign associated with the Brotherhood of Masons, an society of men going back many centuries.  Fortunato realizes that Montresor has not recognized the sign and thus questions him about it.  Montresor says he is a mason, but he is obviously lying.  Fortunato's reply, however, reveals some betrayal of his true feelings towards his "friend".  He clearly feels superior to Montresor by saying "You?  A mason?  Impossible?"  So why treating Montresor as a friend, he betrays this friendship by assuming he himself (Fortunato) is more superior.