Descriptive Problem Summary:
When the person hosting the world is logged into it and is a guest, world.host contains only "Guest", instead of the host's actual key ("Guest-#######").
A related issue is that world.host is set to "Guest" as well (even if the host isn't present in the world) when hosting through Dream Daemon without first being logged in the pager, with DD displaying:
BYOND pager is offline. Connecting as Guest.
In such a situation I would expect the world.host var to simply be 'empty' instead (just as the Reference states).