It’s an induced voltage spike in the camera’s audio circuits, not sound. I don’t know why it’s slightly delayed, maybe that’s just a function of the video compression. The clicks that lightning cause on radio receivers can be used to triangulate lightning location. See http://www.blitzortung.org/en/page_0/index.php
Possibly caused by something flammable in contact with metal oriented perpendicular to the ground discharge. Voltage from a strike decreases on the ground over distance – think of it like ripples from a stone thrown into a pond. The voltage decreases drastically with distance, somewhat concentrically.
Anything that provides a conductive path from closer to further from the strike - the legs of a metal table for example, depending on their orientation - can provide a short circuit which could fry something on or touching it.
An animal or a person standing with more than one foot on the ground can provide the same situation. The orientation of the position of their feet/hooves/paws with respect to the ‘ripples’ can determine their fate and sometimes spares or fells individuals in (what appear to be) random ways. Anecdotally, I’ve heard of a case where someone on horseback (as well as the horse) were killed while the person leading the horse was unhurt.
