No, "Does he like sour cream at dinner" will be "Він любить сметану за вечерею?"
"На вечерю" does sound totally like that's the only thing he's eating (at least to me, don't know about other Ukrainians from other regions). So yeah, it doesn't sound natural :) A little nonsensical, but well, Duo is like that sometimes
As for me (again, my Ukrainian can be different from the Ukrainian spoken in other parts of Ukraine), it does sound like really asking about only sour cream. I would find it weird if to the question "Що ти любиш на вечерю?" (What do you like for dinner?) somebody answered "sour cream". I would ask "Sour cream and what?" or think they're following some crazy diet.