Earlier quoted context omitted.
I'm not sure how he was unable to find their security@google.com email address. Searches like "Google security" and "Google report vulnerability" have http://www.google.com/about/corporate/company/security.html (which has a prominent section on reporting security issues) as their first result.
Because now you know the email is spelled "security@google.com", it would be easy to come up with search query that returns that email address after the fact. If you going by the instinct, search for "google bug report", ...I'm on page 20 and still couldn't find that email. (Personalize search turned off.)
Try searching for "google report security" or "security vulnerability google" and you'll find the right information.