He was high or drunk when he wrote that and it went viral. He probably decided to ride it as people were quoting and praising him for this bold prediction but then had to backtrack so instead of saying he was wrong,he chose the "angry way out" and attacked bitcoiners. Bitcoin is shit according to him, altcoins are better and it was all a lie to pump bitcoin.
Summary? McAfee is an untrustworthy liar, a shitcoin pumper, a celebrity for hire. If he ever had any reputation in the Internet, it's gone now.