The galley is made of Honeycomb structure which contains sealed air pockets.
In addition there are Standard Units still in the galley structure. I don't know how well sealed they are but I imagine that it would be easy to trap (say) 100litres of air in the whole structure.
Hence the galley (liberated from the trolleys) floats. Look how high it is out of the water.
http://i635.photobucket.com/albums/u...Banks/echo.jpg
Why just this galley (5 Trolleys - Door 2?) and not others??????