You can find out who the moderator is through the school campus because since he was a moderator, he had to have some type of status to hold that position of responsibility, it is not something that is just given to anyone.
As to your email, there are a few ways, like WHOIS. Your IP address, unless it is static, permanent, is unlikely. He might have used it by doing a WHOIS from your other address and did a search of your name and found your other email address. Trust me when I say there are ways, many ways of finding things out.
There is a site I find that had where I lived for the past 20 years on it, and it was an open site, not a prepaid site. In today’s world, unless you stay off the network, you have to be very careful of what you put out there and what you say. That is why I don’t have a Facebook, Twitter, or any of those other accounts, and I change my password monthly, more than I do at work and my network at home has four firewalls on it. Call me paranoid, but I am being very careful.