if he registers a new account with fb from his static ip address, e.g. laptop via wi-fi via an isp, fb logs his connection info in their database. the handle, id, or moniker that he creates with the fb account will be tracked to that original registration together with his email address. he needs an email address to register and for fb to send him an email with link to verify or authenticate. that moniker or handle that he creates may be "fookmehard" or some other stupid and seemingly unrecognizable nick but fb can trace that handle to the registration info, and that's when ip addresses are revealed. even if he uses a dynamic ip after registration via a mobile device, his fb nick is unique to his account, and his static ip addresses can still be tracked.
