The fact that Lu Li could use Spirit Casting was quite miraculous.
Demitrian's method of Spirit Casting could be taught to others. According to the design of the game, it needed to be a player with a high level of Charisma and luck. Furthermore, it also needed to be at a time when Demitrian felt that his life was nearing its end. It was only once that these conditions were met that he had a chance at triggering the quest. After this, then there were also a lot of hard work and dedication which only gave him a small chance at learning Spirit Casting.
Lu Li's luck wasn't great and his Charisma levels were also not spectacular either.
That was why it was simply miraculous.