Indeed, who sinned, this man or his parents, that he was born with what they now euphemistically call "delayed intellectual development" (the less polite members of society called him "retarded" to his face) to an abusive father, and died young of a degrading form of incurable cancer whose cause is unknown?
Blaming Adam (or Eve) for genetic defects and cancer isn't helpful; we still have to deal with it. The anger of his father (who is supposed to model God's love and care) and the callousness of people in our so-called "Christian nation" are, of course, a vivid demonstration of Sin with a capital S.
The young man may not have had the intellectual capability understand the problem of theodicy at the philosophical level, but he understood it down at the street level. So, while he believed in God's sovereignty over his suffering, he couldn't see any evidence that God was good or loving or trustworthy, despite my fervent attempts to persuade him that He is.