What does Jeth’s response to Wortman’s question suggest about Jeth’s character and his loyalties?

Jethro is in the general store and for the most part goes unnoticed until one of the men gathered around the fireplace asks his name. When Guy Wortman hear's Jethro's last name, he drunkenly comments on Jethro's brother Bill who has joined the Confederate Army. Jethro becomes angry, and his reaction solidifies our knowledge that he loves his older brother and will remain loyal to him throughout.