It turned out that the details were mostly invalid. Arstechnica did a proper rundown of what occurred, hacker basically just took all the data dumps that have come out over the years (adobe, EA etc) and then removed any address that isnt @google @hotmail @yahoo or @mail.ru, combined what was left and said the logins worked on those mail services.
To his credit some did due to people using the same password on their email as these compromised websites, but it wasn't a hack of these mail services it's just compromised data that has been lingering around the internet for years.
Still everyone should always use a different password for every site and this is a good reason for that