Right.
And because real guns look just like the guns in star wars, there is just no way to tell.
From a distance it might not be so easy.
Actually most of the original trilogy guns (including the storm trooper blaster) were kit bashed onto real guns, and most can be replicated while leaving the gun in working order. Which isn’t saying you should shutdown a school because somebody shows up in costume, but to point out it’s entirely outside the realm that a highly dedicated nut could have a real gun in their SW costume.
Here’s some interesting pics:
http://www.imfdb.org/wiki/Star_Wars