Helaman reminds Moroni of his soldiers’ background. His description of “two thousand” is probably a number that defines a particular type of military unit, and did not necessarily mean that he had precisely two thousand young men under his command. With the addition of sixty more young men, Helaman counts them as two thousand and sixty (Alma 57:19). In spite of the specific appearance of this number, it may still be a military unit composed of more or less than two thousand individuals. (See commentary accompanying Alma 56:27–28 and Helaman, Part 1: Context, Chapter 4, “The Meaning of Numbers: Counts and Estimates in the Book of Mormon.”)
In addition to referring to the size of his military unit, Helaman reminds Moroni, almost certainly unnecessarily, that they are Ammonites and descendants of Lamanites. Why does Helaman remind Moroni of something that Helaman says he already knows? The lineage/political connections of these young men provide a tremendous contrast to their actions. Here are traditional Lamanites who will fight valiantly for the Nephite cause.