Reading Comprehension (RC) | Re: Research concerning happiness and wealth reveals a paradox at any one

For Q3: why A and not C?
A) ungenerous in its view of human nature and mistaken in its interpretation of the evidence.- The author clearly states "This theory may sound good and is commonly heard, but it is not the explanation best supported by the evidence". Hence we can infer that the conclusion drawn was mistaken.
(B) flattering in its implications about human nature but only weakly supported by the available evidence.
(C) plausible in its account of human nature but based largely upon ambiguous evidence - Mind you, the evidence was not ambiguous,nowhere in the paragraphs is it mentioned that the evidence was ambiguous, rather the interpretation or conclusion drwan was wrong.