Possible meanings are 1) "the Zealot" is a title that indicates he was part of the group of people who wanted to free the Jewish people from Roman rule. AT: "patriot" or "nationalist" or 2) "the zealous one" is a description that indicates he was zealous for God to be honored. AT: "passionate"
It may be necessary to explain what "traitor" means in this context. AT: "betrayed his friend" or "turned his friend over to enemies" (usually in return for money paid) or "exposed a friend to danger by telling enemies about him" (See: [[rc://en/ta/man/translate/figs-explicit]])