Basically TOP shows users (yourself) and user processes that you start, on my system if I'm running TOP from a fresh boot it will show one user which is me, but if I start my KVM (which requires admin access to start the VM) it will then show a second user on my system, I may be wrong but I believe it is not just showing physical users that are logged in but processes/tasks that the user owns and has started. ...but I could be totally wrong.
After restarting my computer, and logging in - top is showing 2 users. Next, I started a tty (ctrl + alt + f1), logged in, typed 'exit', and pressed ctrl + alt + f7. Ran top : Now showing 3 users logged in.
I think, possibly, I'm not properly ending my tty session and process.
Its nothing to worry about, each shell you use will count as a user. open a terminal and open another terminal and youll see each count as a user. When you log out a tty it should destroy its self. what 3 users did it show logged in?