They probably think they're being generous: "It's not all your fault that you're the Dajjal -- you were lied to as a child...."
Be that as it may, it is nonetheless a logical contradiction to assert both malice and mistake on the same point.
This lends credibility to the contention that mohammedenism is a mongrel religion cobbled together by illiterates from poorly understood pieces of Judaism and Christianity.
There is a New Testament reference for "deceiving and being deceived," but it is an open ended statement without specificity.