No, it is not a type-setting error! It is an accurate translation of the Hebrew text!
The King James translation incorrectly in inserts, using italic type, the words, “the brother of”. This is an error because the KJV uses italic type for words that are not in the original text, but are implied. In this verse, the words “the brother of” are NOT implied. We simply have an error in the Hebrew Text, and the NASB correctly translates the Hebrew text as it is. Compare:
1 Chron. 20:5 reads, And there was war with the Philistines again, and Elhanan the son of Jair killed Lahmi the brother of Goliath the Gittite, the shaft of whose spear was like a weaver's beam. (NASB, 1995)
The Targum reads, “David, the son of Jesse, a pious man, who rose at midnight to sing praises to God, slew Lachmi, the brother of Goliath, the same day on which he slew Goliath the Gittite, whose spear-staff was like a weaver’s beam.”
ותהי־עוד המלחמה בגוב עם־פלשׁתים ויך אלחנן בן־יערי ארגים בית הלחמי את גלית הגתי ועץ חניתו כמנור ארגים׃
The King James translation incorrectly in inserts, using italic type, the words, “the brother of”. This is an error because the KJV uses italic type for words that are not in the original text, but are implied. In this verse, the words “the brother of” are NOT implied. We simply have an error in the Hebrew Text, and the NASB correctly translates the Hebrew text as it is. Compare:
1 Chron. 20:5 reads, And there was war with the Philistines again, and Elhanan the son of Jair killed Lahmi the brother of Goliath the Gittite, the shaft of whose spear was like a weaver's beam. (NASB, 1995)
The Targum reads, “David, the son of Jesse, a pious man, who rose at midnight to sing praises to God, slew Lachmi, the brother of Goliath, the same day on which he slew Goliath the Gittite, whose spear-staff was like a weaver’s beam.”