Mo Wen was immediately exposed to the moonlight. At the same time, a terrifying aura swept across the heavens and earth, coming closer and closer to him. "Oh no!" Mo Wen muttered to himself. He must have been discovered by an illusionary beast!
When he had chosen this place to hide in earlier, there had been no illusionary beasts anywhere near him. Mo Wen was also confident in his breath holding technique, meaning not even a martial arts grandmaster can discover him if they were far away enough. The only way a martial arts grandmaster could have found him was if they had stumbled across him by also choosing this cave to hide in. That was unlikely.
It must be that Mo Wen had been discovered by an illusionary beast which had approached him without any warning signs at all.