And if the switch has been moved to the "Lock" position then the keypad gets deactivated and therefore the 30 second buzzer that gets triggered when the emergency code is entered would not kick in. The fact that no buzzer was heard likely indicates that the FO toggled to "Lock" as part of his "plan".
In hindsight would if have made sense for the Captain to create a depressurization for that door to get unlocked, possibly by breaking a window?