According to many astronauts, but also based on the photographs of Earth from the surface of the Moon, no human building or construction is visible from there. What someone can see from the Moon is a beautiful colourful and luminous ball, dominated by the ocean blue the, the desert yellow, white clouds and green and brown pieces of ground.
The China Wall is visible, as are other human constructions, from low and medium orbital height, however from the moment that a space vehicle leave its orbit around Earth no human construction is any longer visible.
It is quite possible that the story circulated during the first stages of the American space program, when someone in NASA may have made the statement as a light-headed joke. Another possibility is that Nixon or Kissinger, during their contacts with the Chinese leadership in the early 70s, could have made the statement in a moment of euphoria and in an effort to compliment the Chinese people and its achievements.