Well my guess is because China has the Zodiac signs, and the dragon is supposedly the best one and I think Dragons are sacred in China, so they called it the sleeping dragon. However I Googled it and it said that there was a man named Zhuge Liang and his story is that his reputation as an intelligent and learned scholar grew even while he was living in relative seclusion, earning him the nickname "Wòlóng" which means "Sleeping Dragon" I don't really know what he had to do with China, but that's the best I got! Sorry!
This is because for the past ten years China was very very poor that they have nothing to eat or wear. So that's why it is called the sleeping dragon.
Hope it helps!
Hope it helps!