It looks like the author's first language may be Dutch, where carbon monoxide is "koolmonoxid" and "kool" can mean both "coal" and "carbon" (although there are more specific words for coal such as "steenkool" = "stone carbon").
Coal as in coal power, coal barbecue, and the element carbon use the same word. That’s not a coincidence.
Apart from some exotic forms like diamonds, trees or rabbits (less pure), coal is how we normally encounter carbon.
(But carbon monoxide is "Kohlenmonoxid")
Also graphite. But yeah, coal is basically the purest form of carbon in common bulk usage.