Lin Wu's choice was certainly not something the Twin Lights Liger King had expected. In fact, it was a choice that was not even presented to him. From all that he had learned and observed about Lin Wu till now, the Twin Lights Liger King was sure that he would take over his place.
He did think that there was a small chance that Lin Wu might just turn away, but Lin Wu's personality was not like that. The Twin Lights Liger King knew that Lin Wu also desired power and would like to try his own attempt at this tomb.
The Twin Lights Liger King knew this because he himself was the same as Lin Wu back then. Despite hearing the dangers, he was willing to take the duty into his own hands, because he had the coincidence and hope that he would be able to do it.