No, he shouldn’t comment on a hypothetical question on U.S. policy. However, I’m very uncomfortable with the answer he gave. He could have (should have) just pointedly stated thaat he has no comment regarding such a hypothetical question and left it at that.
He should have said no comment. However, if he said the opposite, that the US would NOT shoot down Israeli planes flying over Iraq, that would be tantamount to saying they already have permission, would create a diplomatic nightmare for dealing with the Arabs and any closet Iranian allies, AND would lose the element of surprise against Iran. He didn’t say we would shoot them down either. He was in a bind and gave the best non-committal answer he could short of “no comment.” You guys should just leave it alone.