Destinys chosen
Even as Lex was experiencing something new, he retained perfect control of his thoughts. He did not allow himself to become too excited, and calmly analyzed the situation.
Although it may not have seemed like it, Lex's progress with arrays was phenomenal. Not only was he memorizing more and more arrays that could be used in various circumstances, he was further familiarizing himself with the new and unique way he designed to form arrays.
He had not had too much of an opportunity to show off what he learned, but just the fact that he could defeat Nascent realm cultivators before his rise in cultivation realm should have been an indication of just how much more he could do with arrays.