To get this joke, you must know that remembering what cards have already been played is an essential skill for playing Bridge well. Any serious Bridge player would know taking notes like this is not allowed.
If you know nothing about the game, you would not believe the levels of anal-retentiveness involved in high-level Bridge. There are elaborate systems of bidding designed to communicate to your partner information about your hand, but there are also rules regarding this, that if you use such a system the other team must be aware of it. I don't really understand it entirely myself.