I know those more knowledgeable about gun proficiency than I am have said this was a very "doable" shot for someone with average-to-better shooting skills and particularly with the use of an optic, but I am still amazed that this wouldn't require a more professionally-trained shooter. But I also think that preparation and practice can improve the odds of success for an average to better shooter.
I wonder whether this shooter attended any previous Kirk events, to get a sense of the typical setup. So knew in advance there would likely be a canopy overhead, Kirk would be seated (thus making a smaller overall target and also a target that is not moving around much), and those event attendees who were at the microphone asking Kirk questions would be off to one side, rather than in front of Kirk.