Without googling, the following should be obvious to any admin.
Shadowed passwords exist as a way to do local authentication with the password not stored in the publically readable passwd file.
NIS exists as a way to centralize authentication across many systems. It moves password checking to a remote system.
The answer that would have suggested that you actually understood what was going on would be to point out that the purpose of shadowed passwords and NIS contradict each other. You either check passwords locally or remotely. Changing how you do it locally when the data is remote is pointless.
The worst possible answer would be to supply large amounts of gratuitous detail (of exactly the kind that you can Google for) without indicating any conceptual grasp of what is going on.
And that is what you did.
Regards,
Ben