Right from the abstract of the first study linked, the authors say that they haven't at all indicated that eating more fruits and veg makes you happier.

"Effects may be bidirectional given that optimists are likely to engage in health behaviors associated with more serum antioxidants, and more serum antioxidants are likely associated with better physical health that enhances optimism."

But I guess "happy people are more likely to eat well" isn't a very interesting headline....