Okay, now it was just a mis-quote:
http://en.f1-live.com/f1/en/headline...28153747.shtml
Hammy says his mistake was just his poor driving that dropped him to 8th at the start of the race... the gearbox failure was purely mechanical.
'Course, with spin on every story as strong in F1 as it is in politics... I'm not sure what to believe. But given the author of the original story saying Hammy hit the neutral button is admitting to have misquoted Lewis, it's probably true that there was a real mechanical failure.