Well, it is possible that Chinese hackers work in large cubicle farms and take lunch breaks which are reflected in their activities. It is also possible that when DEFCON started certain organizations may have treated it as hangout for criminals but have evolved into inviting potential candidates to their private suites where they were wined and dined. It might even be possible that members of such agencies go to computer shows, stop by booths and drop questions like "hey, when you will put a backdoor in your product for us?" and will quietly walk away if the booth people blink or turned down, but start talking if they reached friendly ears. But, these are just urban legends.