I was thinking of the passage at Galatians 1:6-8
" I marvel that YOU are being so quickly removed from the One who called YOU with Christ’s undeserved kindness over to another sort of good news. 7 But it is not another; only there are certain ones who are causing YOU trouble and wanting to pervert the good news about the Christ. 8 However, even if we or an angel out of heaven were to declare to YOU as good news something beyond what we declared to YOU as good news, let him be accursed. 9 As we have said above, I also now say again, Whoever it is that is declaring to YOU as good news something beyond what YOU accepted, let him be accursed."
So that was either hyperbole and irritation on his part and we shouldn't take it or anything else he said in a letter without some careful consideration, or he was seriously out of line in going down that road.