Could it be that the route divers explored != the route the group has taken? So they might have descended using much more difficult route than the one the group took?
Unlikely. I am a Thai so I have been reading a lot of info since the beginning, and most people initially suggest that they shouldn't be in too deep since that Monk junction section is very narrow, steep, and hard to pass, even on foot.
It comes out later that the group frequent this cave many time before.
It comes out later that the group frequent this cave many time before.