“The sons of Caleb son of Jephunneh were Iru, Elah, and Naam. The son of Elah was Kenaz.”
This Caleb is not the son of Hezron but the son of Jephunneh as in Numbers. There were 2 people with the name Jephunneh, but this Jephunneh seems to be part of the Kenizzites, thus the relationship to Kenaz. He is always mentioned as the father of Caleb in Numbers. 2 of the 3 sons of this Caleb, Iru and Naam are only mentioned here. Elah, on the other hand, was a fairly common name, with 6 people sharing 24 occurrences, with most of the citations about the Babylonian Captivity. This Kenaz was the grandson of Caleb, who might have had a brother with the same name.