Sure, the US needs enemies but this is not the case of faking enemy action. This attack was easily traced to Chines devices which were injecting Javascript into HTML files, resulting in a massive DDOS. The servers performing this were part of the Chinese version of Google, which returned contaminated cache pages to queries.
Call me a skeptic, but I don't think the injections were limited to the cache servers Google names. I think this was done at a lower level to achieve the scale. The reason for the attack is somewhat of a mystery as well. China can just block Github, they don't need to DDOS.