But not all these people that knew could ever have been contacted through the work of an evangelist. Some had been living in remote areas of the world for far longer than Christianity. But they too believed in Jesus and God (obviously, they didn't call him Jesus, but they knew who he was). It is proof of the power of God to transcend time and space. God spoke directly to these people. It is the only way they could have known what they did.
please check into the many trips of St. Francis Xavier to India. Could it have spread from someone, say that heard St. Francis Xavier, and then went back to his/her remote village and talked with relatives there?
In my opinion, that would still be the work of the missionary or evangelist. Wouldn't you agree?