Like with the wishes made with the wishing stone, Fred's wish could have been granted in a number of different ways, according to how it was interpreted. After all, he couldn't exist and not have parents at the same time.
So, the wish ended up causing the death of his parents (in a car crash a year earlier), since he wished that he didn't have parents and not that he had never had parents. Now, since he had no legal guardians, he was adopted by another family.
But which family was he now a part of?
