The sentences you listed from your textbook are using the relative pronouns as objects of a preposition, and I agree that they should be used as stated.
However, when not used as a prepositional object, it is proper to use '
que' for both a thing and a person.
I like to call this usage a 'relative conjunction' instead of a relative pronoun. The conjunction introduces a relative clause. Hence, its name. The whole clause is the relative pronoun.
That is what is being used in the two sentences that you find confusing.
The word 'quien' is not a conjunction. Therefore, it cannot be used to introduce a relative clause.
('Prefers' has only one 'r' and no 'e' after the 'r', by the way.
)