My best guess is that this is an AI boy that's wandered the world, mingles randomly with this tribe, and, one of the pygmies, or their associates, happens to be other AI people.? That either includes his father or they help reunite him with his father.? The father explains the situation about the species being in danger and urges him to come help save the day.
But I'm not sure of any of it.? I don't think the pygmies are important though, based on what I think you meant.? Also, I agree with dpg that the term "posthuman" is not universal.? And the "father" of a robot is a confusing concept too.? It's a robot father, so probably not a human robotics engineer.? Still not sure what to take on it.? Here's my take on it:
When a wandering robot boy encounters others of his kind, he learns of their imminent extinction and must help them find a place called the "Promised Land", where they believe they'll be safe.