Rhetorical: We don't immediately see the agenda behind this particular question. Zeezrom is setting Amulek up for a contradiction. By appealing to an angel he must appeal to something other than tradition or the established sources. He is not appealing to a great teacher, to a well-respected person on whom the audience can easily agree should lend weight to the argument. What he has appealed to is mystical, and we cannot tell how well the audience accepted the validity of that experience, though we may assume that they didn't hold it in very high esteem, or the confrontation would not have proceeded to this point.