I seem to remember reading that the FDDOs don't have them holstered, but rather "stowed" in a manner to allow quick access. It it went off, he was messing with it.
Of course that's been known to happen. Back in the very bad old days, Minuteman, and other missile crews, had revolvers that they would strap on at beginning of each "shift" and would not take them off until they were relieved by the next crew.
Of course once the obligatory checks, test and diagnostics are run, it gets boring down in that hole. Several instances of games of "quick draw" were known to have occurred. Until somebody couldn't keep their finger out of the trigger guard of the DOUBLE ACTION REVOLVER, and shot themselves (in the foot IIRC). Henceforth, the pistols were only to be unlocked and strapped on when going to a higher state of alert/DEFCON. ( There was a whole security team "up top" to protect the crew and the Launch Control Facility (LCF) anyway).
Even the SACumsized, steely eyed missile men (each pair directly controlling 10 ICBMs and either 10 or 30 nuclear warhead, and indirectly controlling 40 other bird) have been known to do dumb things... ;(