In truth, Fan Lou could have kept the Light Wind Wolves with him.
If he brought these Light Wind Wolves, who were stronger than him, to meet Lin Yuan, he would kill them. Then, Fan Lou would act surprised, and no one would see through him.
He was completely out of his comfort zone in the Lonely River and was incapable of laying a hand on the Light Wind Wolves, who were stronger than him.
However, logic convinced Fan Lou not to do this because he was afraid it would anger Lin Yuan. If his actions angered Lin Yuan, everything would be for naught!
The Dark Pufferfish wanted to obtain more benefits from Fan Lou. Hence, they would give him sufficient time to ruminate and ensure that his group was safe while they were in the Lonely River.
The Dark Pufferfish knew that Fan Lou and his group had docked on land and were exploring the barren area known as North of the Lonely River.
The Dark Pufferfish did not try to stop them.