wow...how is that cashier not shitting his pants? i'd have to say I wouldn't be so calm in that situation.
Probably because he knows the gun isn't actually loaded. If I can see it out of battery on the film from 15 feet away (camera pov) then the clerk could certainly see it... the thief was just too dumb to realize his gun was jammed probably because he's clueless. At that point it's easier to not shit your pants and just give the guy the money and watch him get lost instead of realizing how stupid he is.
-Mike