Ignorance breeds certainty. As evidenced by his anti-science comments, he doesn't understand critical thinking but what you said resonated with him enough for him to want to have a follow-up with you.
I was baptized when I was 16 and was never more certain of my beliefs. I can't imagine how many times I argued with a much older householder about things I actually knew very little about. Every now and then someone would be in a position to provide a well-thought retort.
Even though I never admitted defeat, those memories stayed with me. As I grew older and my thinking process matured, I was able to revisit some of the points they made. I fought against it and tried my best to repress doubts, they eventually resurfaced.
This young man may never have a change of heart. He may enjoy the comfort that a regimented and structured belief system provides. He may be unwilling to face the real world as it actually is, but you've done your part (and more than I would have likely done). We are all accountable for our own actions, after all.