sentence - Know every words of a passage but not the meaning

A excerpt from 2010: A Space Odyssey 2:

The scientist tapped out a code on the board, switching Sal’s inputs to the memory with the highest security rating. No one knew that he talked to the computer on this circuit as he never could to a human being. No matter that Sal did not really understand more than a fraction of what he said; her responses were so convincing that even her creator was sometimes deceived. As indeed he wished to be: these secret communications helped to preserve his mental equilibrium—perhaps even his sanity.

A little context: Sal is a super AI who accepts human voice instructions, and talks back like having a real conversation between human beings. It is mentioned that she can even pick up her operator’s intonation.

Questions:

1. Providing the context, the communications between "he" and Sal are actually based on talking. So even using the secret circuit, it is obvious that he will talk to Sal a lot. So why it says here no one knew that? Does the thing no one knew refer to the fact that he talked to Sal on this circuit or the fact that he talked to Sal on this circuit because he has trouble communicating with human being?




2. Sentence 3: I don't understand why the punctuation here is semi colon, "no matter" and the words following it is a clause, can clause be separated from other parts of the sentence by a semi colon? Actually, if the semi colon was replaced by a colon, I will have less trouble understanding this sentence.





3. Sentence 3: why does it says here Sal don't understand what he said at all? Or is it just saying that as smart as she appears, the super AI doesn't really understand anything anyone talks to her, not just what he said?




4. Sentence 4: what is that he wished to be? The thing after the colon or the sentence before? And I can't connect this sentence with the previous ones. I know the author is trying to portrait "he" as an isolated computer geek who cares nothing else, but even for a person like that, I don't see why talking to the computer on "a secret circuit" maintains his sanity.

Answer

1. The "as" clause is restrictive, i.e., it defines the kind of talking. You can tell because there's no comma before the clause. So what people didn't realize is that he's talking to a computer in a way that he can't talk to people. As you point out, since he's talking out loud, it's likely that people know he's talking to the computer. And that's hardly surprising, since the computer has a voice interface. What they can't know is the speaker's comfort level with communication.




2. The use of a semicolon is a matter of style. The "No matter" clause really isn't an independent clause as written. It relies on the understanding that it means:

[It was n]o matter that Sal did not really understand more than a
fraction of what he said;

The semicolon indicates that the the clauses are not close enough to combine with a comma but too close to separate with a period. A colon is less frequently used, but when it is, it often indicates that second clause offers evidence for or a conclusion from the first clause:

The man was losing his mind: he was talking to a computer as though
it were a confidante.

3. The passage doesn't say that Sal doesn't understand at all, just that Sal understands little, although she's convinced her creator otherwise. This is just a description of the so-called "Turing test," proposed by computer pioneer Alan Turing. Since we can't really experience what goes on in a computer, we have to say that a computer is intelligent (i.e., it "understands" instead of just "operates") if it can converse with human beings and convince them that they are being understood.




4. He wished to be deceived. It's not the "secret circuit" that preserves his sanity; it's the fact that he can talk openly to someone, or rather something, that understands him.