Well, in story the explanation for the telephaty not finding any info is simply that the demons can't see anything the human sees. They can only hear what the human replies to them. And they can send pictures themself.
So no getting to know humanity from that.
But the point was kinda more: What if revelations was right? So there needed to be an explanation for the low tech the demons and angels had in the revelations of the bible.
As for god. Mad with power and his own propaganda. He didn't use his powers to confirm anything because the thought that anybody even could lie to him never even corssed his mind.