Lex immediately felt the changes, and felt his physique activate as well, yet instead of being alarmed by it, Lex paid more attention to it now. He wanted to gain complete control over his physique so that it would stop randomly being triggered. It had been fine for now, but it could cause him some huge issues down the line.
Since Lex's brain had evolved when he became immortal, now able to directly peer at the secrets of the universe, understand them and comprehend them, it was much easier for him to pick up on things now. He immediately perceived that there was a lot more to physiques than it seemed.
Unlike bloodlines, which had a definitive origin, physiques could occur randomly and did not need a history in one's family tree for it to occur. That meant their origin was not simple, which became evident to him as he observed his physique in action for the first time as an immortal.