I'm pretty sure they can recognize people, and be more calm with those people rather then others. Such as like when my Dad or brother handle my snake, he stays balled up and won't move. But as soon as they leave the room, he uncoils and starts to cruise around. And he never balls up with me.
It's pretty simple conditioning that lets them recognize certin people as not being dangerous. In the wild Big things = Danger so humans are big and = Danger. But after consistant handling they son't see you as such a huge threat anymore.
At least thats my take on it.