Romans 2:12-16 speaks about those who haven't heard the Law of God and how they will be judged according to the law that's written in their hearts. The Bible says that...
God is a just God and what He does is right. When it comes to those who have never heard the Gospel, God will do what is right whatever that is...
Does this seem like a reasonable explanation to you?
If the person asks where's the proof for God/Jesus/Christianity, go here.