Why would King Benjamin talk about themes related to the meaning of his own name?

Matthew L. Bowen explains one wordplay from the discourse of King Benjamin:

Royal sonship is a key theme of Mosiah 1–6, including King Benjamin’s seminal address at the temple in Zarahemla (Mosiah 2–5) on the occasion of his son Mosiah’s enthronement. Benjamin, however, caps this covenant sermon, not with an assertion of his son’s royal status and privileges, but with a radical declaration of his people’s royal rebirth (or adoption) as “the children of Christ, his sons and his daughters” (Mosiah 5:7) and their potential enthronement at God’s “right hand” (5:9). Similar to rhetorical wordplay involving proper names found in the Bible, the Book of Mormon, and other ancient texts, Benjamin’s juxtaposition of “sons”/“daughters” and the “right hand” constitutes a deliberate wordplay on his own name, traditionally taken to mean “son of the right hand.” The name of Christ, rather than Benjamin’s own name, is given to all his people as a new name— a “throne” name. However, he warns them against refusing to take upon them this throne name and thus being found “on the left hand of God” (5:10), a warning that also constitutes an allusion to his name. Benjamin’s ultimate hope is for his people’s royal, divine sonship/daughterhood to be eternally “sealed.”
– Matthew L. Bowen – Becoming Sons and Daughters at God’s Right Hand: King Benjamin Benjamin’s Rhetorical Wordplay on His Own Name

How would Joseph Smith have known the meaning of “Benjamin”?

See:

Matthew L. Bowen – Becoming Sons and Daughters at God’s Right Hand: King Benjamin Benjamin’s Rhetorical Wordplay on His Own Name

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