Ummmm, I'm not sure what wishful-thinking-drug this author has been smoking, but there certainly are HUGE questions about MLK's adherence to scripture, and even if one can rightfully call him a Christian--in a creedal, meaningful sense of the word.
God uses all kinds of people, and certainly King deserves primary credit for the Civil Rights movement of the 50s and 60s in the USA. Just as Jefferson cannot rightly be called a Christian (as he denied the divinity of Christ) and Lincoln too, up until the last year or so of his life denied being a Christian--the social and political greatness of Christian virtues in a man does not make him necessarily a Christian.
MLK denied, in writing while in seminary, essentials such as the Virgin Birth and Jesus' atonement for sin. At one point he was going to convert to Corretta's preferred faith of Unitarianism...but, for civil-rights-strategic reasons (blacks wouldn't follow a unitarian) he became Baptist. There's no way, for example, he could of said the Nicene Creed (or the Apostles Creed), honestly.
Also different lapses in character can be seen--making it hard to consider such a person an active Christian.
King was surely a great man--who did much for America. He was not however...a great Christian man.
In one of the few interviews about his religious beliefs, he denied belief in the Virgin Birth (which was a sort of litmus test in those days to see if you were a “liberal” or a “conservative” in matters of theology).
Ergo, he was not a “fundamentalist”.
He was more a philosopher in the mode of Gandhi.
Nevertheless, he was a great figure, as was Jefferson, etc., though not necessarily a Christian saint.
(Lincoln, btw, experienced a conversion just before Gettysburg; and went from being an agnostic to
a believer.)