So as a pilot and a hobbyist photographer I wasn't able to come up with a definitive answer from google. Virtually all results end up on schlieren photography which is something I've been aware of, but only in controlled settings. I do think it might be the answer here though. The ELI5 answer is that it takes super fast shutter speeds which require a lot of light. This photo is conveniently lit by the sun behind the F-18 which means it is basically a pseudo schlieren setup. Super bright source behind the image but blocked just enough to not bloom it out allowed for the super fast shockwave to be captured. If anyone knows more please feel free to chime in, I would love to learn more on this.