One further observation;

my limited understanding is that this "video" is actually a series of still photos taken by the news photographer, in rapid succession, and not an actual video


It's uploaded to the internet as a GIF, which can be made either from video, or a series of stills. Stills could be why it's jerky, as compared to video compression during the conversion to GIF format. What we see as frames are actually individual photos (as I take it).

There's a gap, missing the draw and leveling of the gun. Goes from reaching into shirt, to gun leveled with shell already ejected in air, and slide slightly out of battery.

Maybe the news crew wanted "dramatic photos" and the camera was flying. But when shooter pulls his gun the photographer might have paused, "*** did he just pull out a gun?"; and then resumes with the gunshot.

Maybe the news crew wanted drama, but wasn't expecting this. If so, they really didn't vet their "security guy" that well.