So, the open carry just happened to be seated in a position in the conference room where the actor playing the assailant highly trained, body-armor wearing SWAT officer/instructor "noticed" him first.
Suuuuure. My money says the "bad-guy" knew who the OCer was. And, even if he didn't, the advanced urban combat training (SWAT) put him high above your average nut-case with a gun.
And, all that aside, we hashed this to death years ago: OCers often OC as social activism, encouraging others to carry by personal, visible demonstration. Those who do made a calculation and decided to take that risk. Too bad the story's author's chose to scare others with a tilted scenario rather than let them decide for themselves by explaining both the pros and cons of OC.