Jiang Yi was indeed trying to comprehend a type of sorcery art. It was the Heaven-Extinguishing Inferno instead of the Art of Plant Spirit.
After trying to study the Art of Plant Spirit for four hours, he realized that he wasn't making any progress. Hence, he went to study the Heaven-Extinguishing Inferno and discovered something mystical.
When he was revolving this sorcery art to absorb the fire elements in heaven and earth, he suddenly had an inspiration. He gathered all the fire elements into his dantian. When he was refining the flames the previous time, he circulated a small amount of Earth Fire into his dantian and found out that it vanished. He wanted to see if these fire elements would also vanish in his dantian.
In the end…
These fire elements turned into a wisp of fire energy and similarly vanished after entering his dantian!
