My 6lb dog has also had terrible inflammatory digestion symptoms in the past, and the culprit was carrageenan, a thickening agent used in many wet foods, so it is not always the main protein/meat content of a food which causes the upset.
I know your dog prefers dry foods, but my dog has Natures Menu raw nuggets for his evening meal every day, and they come in several varieties, including duck, rabbit, venison, all of which may be novel proteins to your one-year-old dog. I take four nuggets from the freezer and put them in the fridge where they defrost by the evening. He has 'wet' food for breakfast.
I strongly suggest keeping a 'food and symptom' diary, noting everything he eats, all the ingredients, and all the reactions he has.
Also, my dog became much more interested in food at 18 months old than when he was 12 months old, and he eats almost anything compared with when he was younger and raised on dry, so your dog may change his preferences over time. He could be anorexic because he connects eating with discomfort and vomiting. I sometimes wonder if some animals know when a food is 'not right' for them, at least I have reason to believe this is possible from my dog and cat, but it's just a theory.
I would give him one food only (no treats or scraps) for a few days to monitor his reaction, otherwise the result will be inconclusive.