Help me understand the basic bone morphing tutorial Example 3

So, I went through the basic bone morphing tutorial and at Example 3, I really don’t get how it’s supposed to work.

The bones in the image / zip file have the opposite direction of what I’d expect (I try to move the foot bone, it will move the whole leg instead), plus I’m not sure how ‘hooks’ would prevent sliding, except maybe by decreasing the influence the foot bone has since the influence is a weighted average of the covering bones.

Any light in this dark tunnel?