They found that the gmail account had information that matched the name and address of the information Comcast provided.

"Chevys@gmail.com was registered to Brian McCarthy at the same Deer Park address Comcast had revealed."

So either the account had information (maybe ip logs but article clearly states name + home address) or it was in the emails.

Hmm, I had read that assuming they were talking about an IP address, but I may have misread it. I think you can put your physical address in somewhere in your Gmail account, but it's not required and I might be misremembering.