Sure? The tail was badly damaged, I am not sure the metal was broken open, and I am pretty sure the hull was intact, eg, the aft bulkhead was not holed.
I think the wings had alot to do with the flotation. The fuel helped, but the voids in the wing provided a good deal of buoyancy. Besides, any modern a/c is pressurized, and designing a device that keeps air in will probably keep water out? The fit on the skin is designed to be tight, since any "leakage" of air, no matter where, means 'drag'? Even the interior penetrations for cabling, ducting and plumbing are sealed, not so much to make her watertight, but to prevent abrasion, and wear on the interior hull.
Not to mention coating the entire a/c with Paint, to lessen drag, an additional benefit would be "watertight". The 1500 pounds of resin/paint have to perform beyond their dead weight, else paint would not be used.
The injured FA was said to have been in knee deep water, at the aft door. I think this intrusion was from the open door, which was then closed? All things considered, an a/c like the 320 is a better boat than alot of boats.