I'm so lost by this question. Was the immortality thing not an eartbending technique??

The text certainly doesn't say its earthbending, and after having read the novels I was really surprised to see online that some fans had gotten that impression. To me it was more like a general spiritual/mediative technique that could be used by a bender or non-bender. The description is vague to be fair and I've come to see how some would theorize its earth, but still really not something that should be said as canon.

The clearest description is basically just a few sentences towards the end of "Questions and Meditations" (pages 234&235)

"With the right mental focus, you could take an inventory of your body and place each little piece that's not where it should be back into the correct order"

"Those who grow, live and die. The stagnant pool is immortal, while the clear flowing river dies an uncountable number of deaths." "I'm trying to teach you about the mind" (emphasis not mine in this case)

So perhaps the best label would a "mental discipline technique". It still sounds kind of spiritual to me. Lao Ge's comments about stagnant pools, and an earlier mention of chakras, remind me of Guru Pathik (a spiritual nonbender who is also quite old).