At Twitter's scale the issues are far less about "this code smells funny" but how dozens of systems interact together. Ain't nobody gonna figure out problems by simply checking out a handful of repositories, and specially in a few hours / days.
I don't know why you think someone would have to know about Twitter's specific implementation of distributed systems in order to inspect those systems for non-twitter-specfifc issues.
Sorry, what was it about my comment you vehemently disagree with?
Such as those which do not meet the standards defined for the particular audit.
Do we know what is or isn't being reviewed? Do we know how much effort is being applied in this process or if there's a defined upper and/or lower bound?