am I right in saying that the incident would not have occurred in the pre 9/11 world as the cockpit door was not locked back then so the door would just be opened manually by the returning crew member ?
Quite correct. Normally, you would simply open a door-knob, like entering any office. And passengers, trying to find the loo, frequently did.
The Indian 737 upset was another security door issue, that nearly ended in catastrophe. The captain had to wait the full 30 seconds, before the door would open on the security code, while the aircraft was basically out of control. Had ther been no security door, control would have been regained 25 seconds earlier.
Aviation safety is always two steps forward, and one step back, as none of the Goons in the CAA ever think things through. TCAS was another, where the Swiss mid-air was a direct consequence of not doing a full analysis of the possible consequences of this new technology - and so a safety measure ends up killing people. Comms frequencies are the same, as I have just illustrated. The number of times I have heard an aircraft go off frequency because of these complicated numbers, at the most inopportune moment, leaving ATC to struggle with a non-responsive aircraft.
Aviation has long been 'Tombstone Engineering', but it looks as though it has now become 'Tombstone Health and Safety' too.