These passwords where probably not stolen from GMail but come from reusing passwords from other websites.

To check out if your account has been leaked: http://isleaked.com/en.php

To search through the ASCII file (only addresses, no passwords): https://mega.co.nz/#!b5lREBgS!LnC9yfR3RC--iMeNMWdQP7m1j4nUf9...

The discussion on reddit: http://www.reddit.com/r/netsec/comments/2fz13q/5_millions_of...