It's odd how they have individual likes and dislikes about what they eat out of. But you can try different materials, metal, ceramic, plastic, etc and different colors too. But I'd try some plates maybe too. It could be he doesn't like to reach over the edge of a bowl to get his food. I had a dog that would only eat/drink out of plastic bowls. And had a horse that would only drink out of blue buckets.
Sometimes there's just no telling...
