Did she overwrote his memories after the death of the father?
And write the "memories" to hide the true circonstances?
In a other story I've read, it was the son who killed the abusive father, and the mother took willingly the blame to hide they fact frol society.
In yet another story (IRL this time) there was this adult who "rewrote" the memories of a kid just after he witnessed a traumatic event. The parent "re-explained" what happend to the shocked kid, and later the modified story became the truth in the kid's mind.