The most famous person of this school is Marcus Aurelius, whose Meditation is very similar to the words in your index in language and thought. He is also a mysterious philosopher who likes to talk about the soul. Moreover, Qian Zhongshu probably read Meditations. Other similar philosophers, such as Plotinus, felt that Qian Zhongshu would not read their books.

Almost certainly, it won't be Socrates, Plato or Aristotle. If so, it will guide their names. It is not mysterious.