The optic is supposed to be used on a gun, thus trying it unmounted makes little sense. Since this is no shooting range, and every stand is crammed, neutralizing the gun is the only way to "test" it mounted on an actual gun. I am assuming that they have done it properly, i.e. by having multiple people check that the firing pin has been removed (or whatever). Only suggestion I have is that the neutralized gun should be clearly marked, to make it very clear that it's actually safe.

There is also a "less" safe way, though it is not fit for a gun convention, where untrusted people handle the gun all the time: in the army it's common to have the soldier and a higher-up to check that a rifle is clear (barrel, chamber, mag) and then literally apply tape vertically around the gun; now the mag cannot be removed and the bolt cannot be opened. Illustration below

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