Respectfully I disagree with you. The terms "pyrokinesis" and "pyrokinetic(s)" were in use at least since the late 1940's, notably in the subgenre of science-fiction treating with "esper" powers caused by mutation of human germ plasm during atomic wars, and some by incidental exposures to radiation during the atomic age of the 20th Century. Many science-fiction writers of the time wrote on this subject (mostly for the pulps), and the best stories of this kind were written by Lewis Padgett, a pseudonym of Henry Kuttner and C. L. Moore. Their anthology "Mutant" is probably the best known and best done of the mutant stories, although to be honest, I cannot say that "pyrokinesis" appeared in any of their stories, but I do know that the word is familiar to me from readings in this period.
It was also in wide use among proprietary spiritualist writings in America and the UK during the 19th Century.
The word itself is likely much older as the ability has been hypothesized and believed in for many years before the 20th Century, and the coining of it would seem to be almost a slam-dunk for any person with minimal knowledge of Greek.
Before you give Mr. King credit for someone else's creation, you should also make him take blame for various 700-page stretches of existential boredom his publishers characterise as "thrillers". The only thing thrilling about King's novels is the anticipated relief of getting to the last page, if you can last that long.
As for pyrokinetic mental powers, I can only say that it must require intense mental effort and probably extended periods of discipline in order to perfect the skill. Frankly I don't have the time for this; I use a Bic-lighter requiring only one thumb, two fingers, and about three seconds of digital manipulation to get a dependable flame, thousands of times. If my Bic is all flicked-out, then I use a match.