At some point, your network assigned StaceysiPhone6s an IP address. Then, your laptop got that IP address. Your Mac then looked up the DHCP logs to find out who 'owned' that IP and found "StaceysiPhone6s". So, it used that info to set the local hostname value.

Example: https://apple.stackexchange.com/questions/30552/os-x-computer-name-not-matching-what-shows-on-terminal