I don’t know much about bridge, but ny understanding is that you can legally “cheat” by embedding information in the plays you make. So I guess there is a kind of tension between basic optimal play and communicating effectively with your partner? Sounds like the kind of thing some hackers would really go for.
Bridge is a game of limited information, and making best use of the available limited information and this included signalling WITH card play, but NOT tone of voice, expression, mannerism, or other such "pokerisms".
For instance "When I lead the Ace of a suit, I promise the king" is legal signaling. "When I hold my cards with 3 fingers I have the king of spades" is not.
It's not cheating if you use allowed information bits (eg card value, not the orientation it was placed on the table) and disclose the systems to your opponents. The bidding also has some rules about allowed systems, but it's the same kind of thing. It's a great game for hackers, but the boomers kind of ruin the fun sometimes.
This is the whole point of the bidding system... Except that it's not cheating, because the other team also has a pretty good idea of what you have as well, because people follow the same systems. The author mentions alerts - this is when you have to explicitly call out the meaning of a bid if it's not following the usual convention. Usually you do this as well as announcing what system you're playing at the start whenever you get a new opponent pair. In his article, he gives examples like "1/2 GF" and because that's not a standard system for tournaments, if e.g. the opener played 1S and their partner replied with 2D, the opener has to alert the other team about the non-standard bid by saying "game forcing" immediately after their partner bids the 2D and before the opponent bids.
This is contrary to the normal rules that you're not allowed to say ANYTHING other than a bid which is a number and a suit. That's why it's surprising on the first page that people are getting upset when he's asking them to be quiet. On the other hand, it's quite common to have a friendly chat during the game as long as it's obvious to everyone it has nothing to do with the game. However, that does obviously open up the possibility of secret information being passed as well as being distracting to the other team, so normally people respect the rules and only talk between games. If people are getting violent when being asked to be quiet during bidding, then they should definitely be told to leave by the organisers.
In terms of secret bidding, I have kind of mixed feelings about this. There are definitely opportunities for creating a very complicated bidding system, and over the years, that's how the main systems evolved, but most tournaments require you to play with specific conventions so that both teams understand the bidding.
In general, revealing the rough balance of your hand to the opponents isn't too big a deal, as if one team has a very strong hand, the other team obviously is in a much weaker position and there's little they can do to stop a win. In desperate measures you might bid something knowing you can't win, but might not lose too badly, in order to stop a massive win, but that's not common. However, understanding the other team's bidding lets you figure out the balance of cards in their hands, so you might be able to defend more strategically if you know they're going for a risky slam.
The real advantage of non-standard bidding systems is being able to communicate intent between "I have nothing and can't support", "with what you've got we can easily make game" and "with what you've got there's a good chance of a slam" as quickly as possible so that there's plenty of bidding space left to explore the details of best suit fit / NT, or to figure out that both teams are quite balanced and get out of the bidding while it's still low.
