Not surprising. Relative humidity (how saturated air is at a given temperature) in east Asia this time of the year is usually close to 100%. Any drop in temperature e.g., by cooling devices, drops the capacity of air to hold water and hence you get condensation and accumulation of water (ever noticed window and automobile air conditioners have drips at their evaporators - these work by transferring energy (heat) from the hot air inside and transfers the energy to the coolant which expands). Most aircraft sit with doors open between flights and get warm quickly. A/C is turned on just before boarding and when you try to cool the hot and humid cabin quickly with no forced ventilation to the outside (a/c are not really equipped to do this), all that water is going to have to go somewhere.

It's just that in flight, the air is so dry (I've seen references of 5-10% relative humidity - the deserts of the S.W. U.S. are around 10-20% RH by comparison) that it pretty much dries out the whole a/c (and not to mention humans onboard).