How are the subsets of classics and history defined? Why are Romance of the Three Kingdoms and Water Margin classified as "Zi"?

Classics are classics, history is history books, philosophers are hundreds, and collection is collection. The Analects of Confucius represents Confucius' remarks and thoughts. Although he didn't write it himself, it also represented his views and thoughts at that time. The Three Kingdoms and Water Margin are works created by people with their own ideas, which are inconsistent with the other three categories. Luo Guanzhong's harmony is equivalent to a "son" with his own thoughts. Zi does not mean that he must be as good as Confucius and Mencius. As long as you have your own theories and opinions, you can call them "Zi".