Okay, I was intrigued and I did some digging. Morton / Z-order is all about interleaving the individual bits of the x and y coordinates. You end up grouping by quadrants. Python one liner:

    points.sort(key=lambda p: sum(((p[0]>>i&1)<<(2*i))|((p[1]>>i&1)<<(2*i+1)) for i in range(16)))