Bitcoin does not evade capital controls.

What the central banks hate is citizens giving the national currency to foreign banks in exchange for foreign currency.  But if a Chinese citizen buys BTC with yuan at Huobi, then sells those BTC for dollars at Bitstamp, the yuan do not leave China.   The net result is that the Chinese got dollars from some American trader, in exchange for "worthless" bitcoins.  That is good for China and bad for the US.  

If those bitcoins were mined in China, that is basically China exporting yet another product made in China.

If those bitcoins are part of the loads that were imported from the West in Nov/2013, then the export trade above would be reversing the loss due to those previous imports.  Depending on the average price that was paid at the time, it may still mean a profit for China's foreign trade balance.

My pet theory for the collapse of MtGOX is that Mark himself bought bitcoins from his customers with non-existing dollars, and sold them at some Chinese exchange, hoping to be able to bring the money out of China at a later date.  But the Dec/2013 decree blocked that transfer...  EDIT: In that case, the trade above would be China selling to Westerners the bitcoins that Mark stole from his clients, and the Chinese government stole from him...