It's time

Even though Lex did not need to breathe to live ever since he became an immortal, and could literally live the rest of his life without taking another breath, he felt a mild sense of suffocation as his lungs began to change.

Taking advantage of the opportunity, Lex activated his right eye, imprinting the very Glyphs and arrays which gave birth to Golden Inferno into the walls of his lungs. His lungs, which were growing strong enough to cause gales and hurricanes, suddenly started to morph in a different direction.

The evolution which was started from his physique, guided in a certain direction by Lex himself, was taken a step further by his cultivation technique. Since Lex's growth using the technique was dependent on his own actions and it saw an opportunity to elevate him based on his own actions, it immediately began to adapt his body.