Mysterious "Staff" account on my school laptop
Staff is the default group that all users on OS X are in. You're simply seeing that 'staff' is the group that's set to have read permissions on your home directory (as it should be).

Although the group has read permissions on that directory, you'll notice that they do not have read permissions on most folders and files within. Here is some additional info on permissions and groups

If you like terminal, you can use the id command to tell if a user is really a user or a group.

id `whoami`