Uptime report multiple users I'm not sure I understand the command "uptime"

uptime
13:58  up 5 days,  9:49, 3 users

I have 3 users detected, but I have only one user account on the Mac and no sharing enabled.

What the users actually are?
Close Terminal.app, then open one Terminal.app window and read the manual pages for uptime, w and who, e.g man uptime, then execute each command e.g. uptime, w and whoin that order in that one Terminal.app window you opened.

It should become apparent however if not... There are always at least two users logged in, you using console and note its time, it's corresponds to the time you logged into your account from the GUI, and you using ttys000 (the Terminal.app windows that you opened). In these instances you is as shown in the output of who am i.

Each additional Terminal window you open will show as another user using , e.g. ttys001, ttys002, etc.