From your link:
Since part of the cave system is seasonally flooded, a sign advising against entering the caves during the rainy season (July–November) is posted at the entrance.[7]
They entered the cave in June.
It is weather and as such does not confirm strictly to a schedule. BBC reports that the Indian Ocean is producing systems. The cave is already flooded, and today there was significant rainfall. The general concensus is the the monsoon season has arrived. The heaviest rainfall is usually in August/September.
LOL!