Pi didn't understand, Zhang Zian didn't either.
Yes, he had already guessed Pi's origin a long time ago, but that was because there were so few thought experiments that involved monkeys, it was easy to guess. The problem was, what did have to do with the untitled book or Archimedes Constant?
Zhang Zian didn't know the answer to the riddle, so he didn't give one. Just like how detectives need conclusive evidence before testifying against a criminal, Zhang Zian needed information before answering the riddle.
There were many monkeys that could type, so why did Pi stand out?
Until today, the answer had always puzzled him.
Now Zhang Zian knew, it had to be Pi.
Zhang Zian saw Pi delete Archimedes Constant, as well as a look of hopelessness on Pi's face. Zhang Zian didn't want Pi to be depressed again, so he stood up. It was time to make Pi understand.