It's a Bible reference. Jesus supposedly said that "A prophet is honored everywhere except in his own hometown and among his own family". When you grew up with someone everything will be colored by your past experience with them. You remember all the grandiose stupid things they said in the past. If they are saying actually wise things now you will not believe them as much as you should. On the other hand if they are still saying stupid things other people have not yet learned caution.
I guess the connection is that when you're far away from home you can project an aura of confidence/respectability that you may not have at home where people know you since the days you were not yet an expert.
Of course people can't be born experts and for every expert there must be a prior step in their personal growth when they were less expert. But that doesn't prevent people from using an imperfect heuristic for judging whether you can trust someone's expertise.
It's possible. I don't know. Sometimes people just come up with the same ideas over and over.
Classic example is the pyramid structures around the world. The fact that people found that it's easy to pile rocks that way in order to build tall stable structures doesn't mean that there was a single culture that span the entire globe.
