A lot of the writing in the book is told in 1st person narrative, with two of the main writers, as well as a couple more minor characters, having the name Nephi. Lends itself to a lot of "And I, Nephi, said..." Also, the name was given to a city that is referenced several times, and to the land the city was in... It adds up.
I love these kind of quizzes. Really force you to think of super common, non-obvious words. I would think, in regards to the having 74 of the same words as the Bible version of this quiz, that most books/writings in general would have a high concordance rate. Besides such inclusions as "Lord" and "God" and all the thee's, thy's, and thou's, most of the words are pretty commonly used.