Zenock was a brass plate prophet who is not present in the Old Testament. Ezias might be a different transliteration of the name we know as Esaias:
“Elder Orson Pratt suggests that “Ezias may have been identical with Esaias, who lived contemporary with Abraham.” (See D&C 84:11-13 .) (George Reynolds and Janne M. Sjodahl, Commentary on the Book of Mormon, edited and arranged by Philip C. Reynolds, 7 vols. [Salt Lake City: Deseret Book Co., 1955-1961], 5: 272.)
Since the name is coupled with that of Zenock, it is also possible that this is a name from the brass plates for which we have on this single reference.
When Nephi cites Jeremiah he cites Jeremiah as having a known fulfilled prophecy, that of the destruction of Jerusalem. It is interesting that Nephi would use this particular fulfillment, as the Nephite knowledge of the fulfillment comes through Lehi’s prophecy, not actual knowledge.
What this tells us of the Nephites is that even amidst their apostasy from the general principles of the gospel, they do retain some basic beliefs. They accept the brass plates, and they accept the founding traditions of their people, which included the destruction of Jerusalem as the reason the founding family left that area. Unlike Laman and Lemuel who doubted, the longstanding tradition of this people was one of belief in the destruction, so much so that Nephi could use it as a demonstration of the fulfillment of prophecy.