Yes! _Thanks!_ This is the first time I've seen a plausible explanation for a lit torch in a cave! Have you noticed that they just show up otherwise? Here we've seen enough to know there's random items on the floor. Sun Bao has brought his wuxia lighter* and it's logical that he finds a torch to light with it
Now I expect skeletons!
(*Ubiquitous in wuxia - originally a small bamboo pipe carrying embers cleverly embedded in stuff to stay glowing.)
