I can imagine plenty of circumstances where a woman might quite reasonably feel at the time that the best option, for the child as well as herself, was to accept as the father the man who "gets the idea he is the father of the child". From Wolfgang's scenario it would seem probable enough that in fact she'd have have thought he likely was the father.
And he got a daughter out of it. So what if it turned out years later that the child that saw him as her father wasn't his biological daughter?
I can't see how finding out something like that could in any way interfere with how you felt about the child. It might make you feel different toward the mother, but then that relationship is over anyway apparently in this scenario. How could anyone want to get back at the mother badly enough to hurt their own child?
Well, true enough some men are like that. Right bastards they are too.