You don't know that. They are shipped to San Jose, California, where they are inspected by SuperMicro. They have also been inspected by the manufacturers of the servers. . . much more so since this story has broken and not a single compromised server motherboard has been found. Not one, out of millions. NONE.
Both Apple and Amazon installed these specialized servers in their STREAMING VIDEO services. They are NOT used for generalized Cloud services. Streaming video is what Elemental Systems makes. . . and that is where supposedly these motherboards were intended to be installed. . . and what these high speed SuperMicro motherboards were designed feed. High Speed streaming video, not more mundane data which does NOT require handling large high-speed data dumps to multiple threads simultaneously. These were specialized for video. Amazon was installing them for Amazon Prime video and Apple was installing them for iTunes Movie and Video service. What was China going to get? Copies of old "I Love Lucy" episodes and the latest releases of last summer's movies, or Amazon Prime's dedicated content? There would have been little else on these feeds going through these motherboards to steal.
LOL!
ALL modern manufacturing incorporates QA at the factory. I guess if someone had absolutely no knowledge at all of production they could say otherwise.
Or they could just be being silly to be silly.