What do you call someone that gives you an answer to a question that doesn't explain why they dislike something?

Solution 1:

A person or an answer can be unhelpful, and an answer can be unsatisfactory. These are judgements by the listener and usually do not address the speaker's intent (unless we say that an answer or person is, for example, deliberately unhelpful).

If someone is intentionally avoiding a direct answer, we can say that they or the answer is evasive.

evasive

If you describe someone as evasive, you mean that they deliberately avoid giving clear direct answers to questions.
He was evasive about the circumstances of his first meeting with Stanley Dean. Collins

Tending to avoid commitment or self-revelation, especially by responding only indirectly.
‘she was evasive about her phone number’ Lexico

In this dilemma they thought it safest to give an evasive answer, of friendly sentiment towards both parties, but refusal of aid to either; hoping thus to avoid an inexpiable breach, whichever way the ultimate success might turn. ref

Someone can avoid being overtly critical or negative by giving an answer that is (overly/too) tactful.

tactful

having or showing tact m-w

tact a keen sense of what to do or say in order to maintain good relations with others or avoid offense m-w

Undoubtedly Post is right that a tactful person would not say that the room is hideous after it is finished. Although she doesn't give examples of a more tactful answer, we can probably come up with our own ideas: "That's a really bold color scheme" or, "I especially like that lamp over in the corner." ref.