Guding's virology course only lasted one semester because the virology professor suddenly resigned, and the military academy couldn't find a second virology teacher, so the course was left incomplete.
Later, Guding also heard some rumors about the teacher, who was said to have been quite renowned in the Cosmic Sea despite his unremarkable appearance. Guding always just listened to these rumors and never took them seriously.
For him, the old man's identity wasn't important. What mattered was that despite initially having no interest in virology, he developed a keen interest after attending the old man's lectures. So much so that after the academy suspended the course, Guding still occasionally went to the library to look up virology related materials.
Since virology is a branch of pharmacology, Guding wasn't opposed to becoming a pharmacist.