There is no other explanation for this boxy superstructure otherwise. It is a hangar, and a very big one at that.That large-size helicopter landing pad relative to the size of the warship itself probably means that it can operate not just Z-9, but probably Z-20 as well. Though, until the warship can be seen from the rear, I don't think there will be a helicopter hangar onboard.
So big in fact, that imho that smells of composite superstructure - though this is of course a guess.
The biggest (?)s right now are probably underwater hull shape, p/plant and speed - as indicators of role and displacement.
But my current guess(asi wrote in 056 thread) is probably sino-LCS: reasonably survivable, numerous, and fast surface combatant for stand-in missions in contested space.