I gave a short time working as a GM back in late vanilla / early TBC (which is where I first saw multiboxing and decided to try it), those sort of bans were also handed out to people who had multiple cross faction accounts on pvp realms if they interacted with each other... even if someone your grouped up with kills your opposite faction account and not you directly. People used to guild farm alt accounts to try and beat the hardcore pvp people who spent 12hours a day in pvp for three months to get to rank 14. Problem they had was it used to track your IP address of accounts not account names, so if your brother had his account you could get false flagged for killing him yourself, and there was a generic (economy/honor) email generated and sent to those players.