There is another explanation. In Professor Ceng Shiqiang's The Mystery of the Book of Changes, Professor Ceng Shiqiang means: I know one thing for those who know, but I don't know one thing for those who don't. My understanding is that different people have different answers. Professor Ceng Shiqiang gave an example of a student of Confucius betting with a grasshopper. The grasshopper says there are three seasons in a year, and Confucius' students say there are four seasons. Later, they asked Confucius together. Confucius looked at the grasshoppers and told them that there are three seasons in a year. After the grasshopper left, Confucius' students asked why. Confucius said that grasshoppers don't live in autumn, so for him, there are three seasons in a year, and there are still three seasons for you to fight with him. So "knowing means knowing, and not knowing means not knowing" should mean that "knowing some knowledge" is for people/things who "know this knowledge". (knowing is knowing), and the second half is the same.
Tell everyone to study with an open mind and don't pretend to understand. It shows that Confucius' attitude towards academics is not fraudulent and honest.