My definition of "intelligent" is native cognitive capacity. My definition of "stupid" is the failure to use one's intelligence.

I consider myself to be relatively intelligent and yet I am not immune to being stupid.

Because my friend is a devout evangelical (his father was a preacher), he's been deeply indoctrinated. It's my contention that religion by design makes one stupid: "do not question things, respect authority".

In evangelical circles it's my understanding that children are indoctrinated to treat "outsiders" as ungodly and to be avoided, let alone engaged with. This lines up with his behavior too.