Another possibility - perhaps someone with an ethical mindset released it prematurely to draw attention to the bioweapon operation before it became a huge problem. In other words, released it prematurely, knowing that although it would cause harm, in the long run, it would cause way less harm than if China had continued developing it to its desired lethality.
I just wandered around twitterland for a short while and am more convinced it was accidental, whatever way it was. I will post a bunch of twitters later today about this and other stuff.
I like it! Maybe the Chicomms kidnapped a person from Hong Kong and made them work there and the released it.