Shui Yuan knew Lu Ye had a dragon scale because she had seen him refine his body using the blood Qi energy within that dragon scale.
At that time, she had inquired about the origin of the dragon scale, and Lu Ye naturally didn't hide it.
Shui Yuan then speculated that there might be some hidden secrets or opportunities beneath Dragon Spring.
Lu Ye had already made up his mind that once his cultivation in the Spirit Stream Realm reached its limit, he would definitely make a trip to Hundred Peaks Mountain to see if he could obtain more dragon scales.
Mount Qingyu, Tailuo Sect, and the Qin family, although they had occupied Dragon Spring for so many years, they probably were unaware of what lay beneath it, otherwise, they would have started exploring long ago.
In other words, the dragon scale that Lu Ye obtained might be the only one.