Your response to the man who asked about the salvation of one who has never heard of Jesus begs the question.
You wrote that God puts an awareness of “His eternal power and Godhead” in the mind and heart of all His creation, which I believe.
But that is not the same as the, can we say, “technical” aspect that salvation comes only through belief in the death and resurrection of Jesus, the Son of God, whose blood pays the penalty for our sins, which I also believe.
Thus, a wild man of Borneo may know of God and, after his fashion, worship Him as Creator, but still not know, having never heard, that God came to earth in the person of Jesus, lived a perfect life, and shed his blood that all who believe this and come to him will be saved.
How can he know “without a teacher?”
That, I think, is the man’s question, and mine as well. Will the “wild man” who believes in God, but who never heard of Jesus and who, thus, is unable to come to Him, be damned?
There are several basic things we know about God that have to be reconciled to one another to answer this question.
1) Man is without excuse (Romans 1:18-20).
2) No one comes to the Father except through the Son (John 14:6).
3) God doesn’t want any to perish but all to come to repentance (2 Peter 3:9).
4) All who call on the name of the Lord will be saved (Romans 10:13)
5) God is just and can not condemn someone who could not have known how to be saved. (2 Peter 2:9)
When you put them all together you have to conclude that once a man realizes that God exists and acknowledges Him as such, then God will move Heaven and Earth to show him the way to salvation so he can make an informed decision. We may not understand how that happens, but to deny that it does is to accuse God of being unjust.