The passage argues that the memoir that Chevalier wrote are fairly controversial which is lack of accuracy. The professor holds a totally different view what the Chevalier wrote in his memoir are all true and can be explained by some decent evidences. 
Firstly, the passage states that the writer is wealthy when he was in Switzerland while he put a great deal of money on the gamebling and parties, whereas some evidences reveal that he had borrowed much money from Swiss merchant. However, the lecture points out that it is indeed likely that he sell his property firstly, but it's proper to take some time to convert what he sell to the money. That's why he need to borrow money from merchants until his own money arrived.
Secondly, the passage claims that he hadn't been conversing with Voltaire, so it's not likely for him to write an accurate book about their conversations with details. The lecture refutes the idea completely, and professor explains that he has been living with Voltaire in the latter year. It should confirm that he has been regularly consulting with Voltaire about journals when he was writing the memoir.
Thirdly, according to the passage, it's impossible for him to run away from ceiling since he had lots of  politically well-connected friends in Venice who could have offered a bribe for him. The lecture argues against passage that there were lots of people who have much more powerful friends than he had, but they were not able to stay away from the jail. According to the government document, the ceiling of jail was needed to repair due to the broken which can striongly support that Chevalier had been successfully run away by himself.