1) Because the spin is even. Both the amount of protons and the amount of neutrons is odd. I think we can even say that there are 2 more protons than neutrons, or 2 more neutrons than protons? And due to the integer spin, the atom will behave as a boson. Also, the spin-up corresponds to the lowest energy and vice versa. And spin orientation zero gives no energy difference, So the atoms are in a magnetic field, with the direction of the field pointing upwards?
2) A system will try to be in its lowest state of energy. Here a low energy atom corresponds to m=+1 or the atom being orientated upwards. So most atoms will be orientated upwards or looking at the previous video. A sort of upside down pear.