China has a history of inflating economic performance indicators. Massive overestimation of grain yields was one of the key factors contributing to the Great Chinese Famine [0] [1]. It wouldn't be surprising if this would still be the case.
I think comparing the state of China during and after Maoism, especially after the advent of Deng Xiaoping as head of state during the 70s, is a completely unfair comparison. It really speaks a lot to the understanding us westerners have of actual Chinese politics.
[0]: https://en.wikipedia.org/wiki/Great_Chinese_Famine
[1]: http://www.missedinhistory.com/blog/missed-in-history-the-gr...