Arnold denied being a prophet. He was just wrong, as we all are on occasion.
Are you being deliberately obtuse?
Murray said that the AntiChrist would appear in 1981. That is a prophecy.
It didn't happen, which makes him a false prophet. When a person sets himself up as a Christian leader and starts predicting endtimes events, it's much more serious than merely "being wrong." Doesn't matter how much he denied it.
Speaking of setting himself up as a leader, before I forget it, let me note that Murray claimed he had a doctorate degree. He was later proven to be lying.
Apostasy means giving up or renouncing of one's professed principles, or faith. This will come to pass when the religious lamb (false messiah) of Revelation 13:11 comes to pass. He will look like the Lamb of God, but his voice is of the dragon, for he is the great dragon, that old serpent, called the Devil and Satan (Revelation 12:9). When the false christ stands in the holy place performing in the sight of Christians, the pretribulation-rapture-Christian shall think it is Jesus Christ coming to rapture them away. It is the duty of the elect to stand and witness in the synagogues, allowing the Holy Spirit to give His Message to the world through you. (Mark 13:9).
Jesus Christ is your spiritual Husband. You should remain a spiritual virgin until He returns (II Corinthians 11:2). For Jesus Christ Himself said; "Woe to them that are with child in those days!" (Mark 13:17). If your spiritual Husband has been on a long journey and finds you with child when He returns, then you have been impregnated (deceived) with the mark of the false messiah, and worshipped Satan in the last hour. Study God's Word. http://www.shepherdschapel.com/statement-of-faith.cfm
He's just wrong, very wrong about this, too.
However a prophet proclaiming God’s Truth cannot be wrong. There are more verses in Scriptures on God’s burning anger towards false prophets who say they are proclaiming His Truth than one verse in Romans 11 which is clearly taken out of context.