The cheapest somewhat predictive model for the other humans is that they're just you.
This is why young children fail the Smarties test. They now know the tube has a pencil in it, therefore under this simplified model other children know the tube has a pencil in it and that's the assumption they report when asked.
But under this model if I believe something then that's what you believe too, and if you deny it then you are definitely lying. Loads of Americans resolutely believe that all humans know the Christian God is real, and it follows (under the too simple model) that whatever it is they believe about that God is necessarily apparent to everybody in the world, therefore anybody who says otherwise must be lying.
This is why young children fail the Smarties test. They now know the tube has a pencil in it, therefore under this simplified model other children know the tube has a pencil in it and that's the assumption they report when asked.
But under this model if I believe something then that's what you believe too, and if you deny it then you are definitely lying. Loads of Americans resolutely believe that all humans know the Christian God is real, and it follows (under the too simple model) that whatever it is they believe about that God is necessarily apparent to everybody in the world, therefore anybody who says otherwise must be lying.