A full-screen appearance mode can be turned on by using function keys, in
some of what I've read; this is sometimes referred to as 'kiosk mode'
while that is a misnomer because there are other documented ways to have
a Mac run in a more purely "kiosk" situation; this has been around for years.
However the simpler forms of this usually involve browsers or other apps
which can use a basic keyboard shortcut. A 'true kiosk mode' may require
an alteration within the software, or a companion application to engage it.
Accidentally engaged it? There is a high unlikelihood of sophistication in
arriving at that situation; it probably is not running a true 'kiosk' mode.
To escape whatever it is, you may try starting up in SafeBoot mode, and
then read the Console logs of the time when the person was using the Mac.
{I've found tons of relevant 'kiosk' related information, in google search;
I remember seeing G3 iMacs running in full kiosk mode, when sold new.
They even had touch-screen technologies for retail, to use CRT access.}
Some browsers used to be able to go into 'full-screen' mode through use
of function keys; such as F-11. Not sure what app the computer was using
but the field of difficulty limits the probability of how this was done.
The big search that gets me more results than apply in this instance, uses
the words ' *mac os x help: use mac in kiosk* ' - in google search.
There was a mention among others, of a way to use Parental controls to
engage a type of kiosk-like mode; but I did not read into those. I remember
seeing demos of kiosk mode Macs, starting way back in OS 9, in retail.
And that was in a small AK reseller's shop. Also, a few malls had them.
Hopefully some of this helps. I think a restart, especially if you have more
than one user account, could resolve this main issue. You may be able to
use the escape key or other command to get the display normal, too.
iTunes player can go full screen (and back) with simple commands, etc.
Good luck & happy computing! 🙂
