I'm sure the Captain new how to open the door! The usual way by pressing # and waiting until the door is unlocked, or by entering the emergency code and waiting for the time lapse to be over.
However, due to the way he had conducted himself in the flight deck... We can assume the First Officer used his "superior CRM skills" to get the Captain out of the flight deck and then use the "deny" function of the CDLS thus preventing the keypad from having any further effect (normally set to inhibit the keypad for 5 mins)
From then on the Flightdeck door and entry procedures did exactly what they were designed to do.