Life Qi!
Randeng spoke with absolute certainty.
In fact, he could also be considered a demon corpse that had achieved enlightenment.
The so-called "Spirit Coffin" actually refers to the coffin in which the dead have been placed for burial.
Back then, Randeng was nothing more than a dead thing. However, he accidentally devoured the ever-burning "Ling Shu Lamp" that was near him, which led to the formation of consciousness and, eventually, his transformation into form.
It could be said that Randeng had an extremely strong feeling towards both Death Qi and Life Qi.
The bigger reason for him being the past Buddha of Buddhism was precisely because he had achieved enlightenment as a "Spirit Coffin," being essentially a dead object.
Death represents the past, life represents the present, and surviving constitutes the future.