How to determine the right K points for the band structure of a slab?

I am trying to compare the band structure of a slab and the bulk phase, just like the example on the VASP wiki. In the example of VASP, it calculates the band structure of the slab of Ni metal.

A slab is basically a crystal that has a new kind of symmetry, but the example doesn’t generate K-points from the slab, it uses the K points extracted from the Brillouin zone of the bulk primitive cell. I am not sure if this is appropriate.

And I should follow the way in the example, why should I choose K points from the one facet of the Brillouin Zone of bulk phase?

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