I can't really explain it. It was a puzzle to all of the interviewers.
The only reasonable hypothesis I have where I assume the candidate was honest is that the quality of the code in his github profile is largely due to help from others.
Or that they are bad with on-the-spot-questions-with-short-time-limit-while-every-move-under-scrutiny-by-potential-employer situations ... Which usually only ever happen in interviews.
The only reason I can do well in one of these interviews is because I recently started writing poor patch code for websites.
In development, who would do design, code and review on only one change in a straight sequence? It is like asking half your brain to shut down and the gods to smite you.
The only reasonable hypothesis I have where I assume the candidate was honest is that the quality of the code in his github profile is largely due to help from others.