Every data packet that your router sends or receives to anywhere on earth has the IP attached.
A typical visit to the bb from any user probably generates an average of 100 packets. (Every one of those is logged in the history file by line.) So if my server receives a packet that is anything to do with this (or any other bb) its pretty easy to pickup the address.

It wasn't actually something Greg set-up, it was an option always available in the software that he chose to switch on.