A very oversimplified explanation that is easy to understand...
Umm, he's holding a Charcoal Briquette made from Wood & used for grilling...
I have seen actual coal both throughout my childhood and used it for heat for 25+ years as an adult.....so this guy is at a minimum incredibly lazy or maybe trying to delude people??
WTF????????
@Garban Exactly! We used anthracite, 3/4" (it comes in sizes just like gravel.) Pieces are shiny, hard, can be sharp, and have similar weight to a same-sized rock.