Seriously, this kind of stuff doesn't really happen. You don't send 1300 people's passwords and details away via email "by mistake". It'll take significant effort even getting that information, and it's not something you would email at all, to anyone (so no, "I sent to the wrong address" excuses).

Someone's trying to do something big there, and got caught. And how did the sender know the email account? Definitely not a random guess. Thus I question the innocence of the email address holder...