Conviction: a fixed or firm belief [dictionary.com]; a strong opinion or belief [Cambridge Dictionary].

Atheism: the doctrine or belief that there is no God [dictionary.com]; the belief that God does not exist [Cambridge Dictionary].

Also, "this person's" father was an atheist, he studied philosophy, and was in-and-out of addiction recovery programs throughout adulthood. He likely had more insight into the minds of non-religious, religious, and whatever people than you're giving him credit for.