Are his teeth okay (you can’t tell by looking). When was his last dental exam? Dental x-rays? They can have root remnants that need extraction, this can cause pain, not visible until the cleaning is underway and x-rays are done (general anesthesia) They are usually in and of the vet clinic the same day, within a few hours.
I ask because I have had several small breeds and none of them had any trouble eating kibble regardless of the size, unless they had periodontal disease and needed a professional dental cleaning and extractions.
That being said, some dogs do better if the kibble is presoaked in water prior to serving, or maybe the dog would prefer soft/canned food.
