I don't know what you mean by "judging people by appearances", how is that relevant? I haven't read the bible, I personally ma not a Christian. I just grew up in Christian culture. And infosec presumably also predominantly developed in that culture, as it was dominating the Western world for wuite a while.
I don't think the bible says brides should be dressed in white, nevertheless it seems to be a common Christian tradition.
So no, it was not "picked out of nowhere", after all Christian religion was what has defined good and evil for hundreds of years now, in the world in which infosec developed.