@Cubs2Jets,
Those are not "outflow valves", in the picture you posted, but pressure relief valves on the pressure bulkhead. The (single) outflow valve on an A320 is mounted on the fuselage further fwd, just behind the aft bulkhead of the bulk cargo area. Those two relief valves shown, would in all likelihood have remained closed.
The ditching switch (which was not used) would have closed the two fwd avionics cooling valves as well as the outflow valve.
Personally, I wonder if water rushing in the open outflow vlv during ditching might have had something to do with the damage to the aft pressure bulkhead?
In any case, the aircraft floated because of all the air in the wings. The fuel tanks vent out the bottom, so the air was trapped.