It's never easy to read these gauges.
Above 50, as noted, means expansion.
So today's reading of 50.2 is a plus sign for China's economy.
However, some of the underlying figures or 'internals' showed a reading of below 50, of particular note new export orders, which recorded a reading of 48.2.
This is where we get bogged down in the old 'slowing growth' vs. 'less fast growth' debate.
The bulls, such as Michael Pascoe at SMH, will argue that China's economic growth rate slowing from 8% to 7.5% is a good thing for stability, particularly since each year the economy is significantly larger than in the preceding year.
In other words, 7.5% this year, means greater growth than 7.5% last year did.
Similarly, AMP's Chief Economist Shane Oliver normally retains a sanguine outlook on most matters China and otherwise.
He sees China's growth continuing at ~7.5% or so, which is precisely what Australia wants, since that represents an ever-growing demand for our resources.
Edit: Pascoe's view: