China is pretty good at being tight lipped about any terrorism that goes on within their borders. There are a few examples that have leaked out, but not many.
If you think about it, because they are fast and loose with the safety standards, they have set themselves up for the possibility of a terrorist taking advantage of the situation.
Now couple that with some rumors about their economy and the "investment’ (voluntary or regulated) of large amounts of retirement accounts in to the national markets (which are tanking) you have an additional reason for discontent and the seeds of terror.
Is it a possibility? I would say that the third time it happens it may be something to really look hard at.
With their economy growing as fast as it is they may have reached the point at which they begin using the crap they make for export in their own stuff.
This looks smaller than the last two. Not sure how frequent blasts of this size have been in China anyway with their lax safety standards. But it seems like a lot in a short period of time.