How did the commentator of Bukhari know that those who were with Abu Barzah were fighting for worldly gain, and does this imply hypocrisy?

This statement was presented by Al-Ayni to explain the meaning of the Hadith (definition) of Abu Barzah Al-Aslami; he did not offer it as his own ijtihad (definition) (independent reasoning). Abu Barzah made this statement when he witnessed their state of fighting over the matter of the caliphate and their contention for it. Ibn Battal said: "As for Abu Barzah's statement: 'Indeed, I seek recompense from Allah that I have become displeased with the living tribes of Quraysh,' the reason for its consistency with the translation is that he did not say this when Marwan pledged allegiance to him; rather, he pledged allegiance and followed, then became displeased with it later on." This statement from Abu Barzah is his own ijtihad, and the principle is to refrain from discussing the disputes that occurred among the Prophet's Companions, and to believe that they are either a mujtahid who is correct and receives two rewards, or a mujtahid who errs and receives one reward.