the article doesn't mention that you have to confirm your email is valid by clicking a link before you get registered so incriminating strangers this way should be impossible. I presume he validated the email himself
> It’s important to note that Ashley Madison’s sign-up process does not require verification of an email address to set up an account, so legitimate addresses might have been hijacked and used by some members of the site. One email in the data dump, for example, appears to belong to former UK Prime Minister (Tony Blair).
-- http://www.wired.com/2015/08/happened-hackers-posted-stolen-...