Shamelessly quoting Tyler Cowen's summary of Alwyn Young:

The Chinese economy has indeed done well. But once we cut through the mysteries of the numbers, we find an explicable reality. The Chinese growth experience is in reality comprised of "reasonable and comprehensible" numbers, rather than miracles. Young even wonders if the Chinese could not have done better than they did. On one hand, most economies would be delighted with a sustained 2.6 percent rate of labor productivity growth. But on the other hand, China has been moving away from a centrally planned economy. We might have expected even larger productivity boosts, given the incentive benefits of economic freedom. We also can interpret the figures as showing that China has enduring problems, and has not moved as far away from central planning as we might wish.

So it's no miracle.