AFAIK there are no door flt locks on the Airbus 320 series CEO. It is called a plug door because when it is shut the differential pressure pushes the lugs on the door against corresponding lugs on the airframe. On descent and approach the differential pressure equalises with ambient pressure to allow the doors to be opened in the event of an emergency.
I'm still impressed that the door assist system was able to open the door against the airflow though.
Could have been a whole lot worse if the slide had ended up wrapped around the tail section.