[danilocesar]

Think about thin vertical passages. You can talk trough them easily but diving would be very difficult.

I know nothing about that cave, but passages between caves can be connected by tight restrictions. They might have crawled they way up. And now that restriction is flooded.

[wepple]

Add a bunch of regulator hoses, fins, air supply etc to someone not used to having them attached and the gap needs to be huge to not snare a hose and rip a full face mask off.

Even a semi experienced diver is far less aware of all their apparatus than a human who has been crawling around things since birth