Xiao Changfeng was worried about our safety. Perhaps he vaguely sensed that we intended to act alone, so he returned quickly.
Without the password or 'key' to open the door, he deduced the mechanism of the cave entrance by listening to the echo of the knocks and mapping it out.
The chip in his brain wasn't installed in vain; some things that ordinary people can't do, his enhanced brain can achieve.
Xiao Changfeng and Gan Quan saw the corpse of the Big-headed Bird in the upper layer and slid down the vertical shaft with a rope lock to the underground river.
This forced them to retreat. After measuring the water flow and river direction, they came back down with equipment.
It's unrealistic to go upstream by personal strength alone, let alone climb a waterfall cliff barehanded.
