That's very curious. How old was he?
Was he fed the same as the hens his whole life?
Chickens have 2 kidneys with 3 segments each. Some respiratory diseases as well as excessive calcium in the diet can damage those segments. They can become atrophied or enlarged. I would think the state vet, if a trained avian/poultry pathologist, would know that.
He was under a year old, and we fed him flock raiser crumbles, so he should not have gotten excess calcium. The state vet wasn’t the one who did the necropsy, it was some poultry specialist at Cornell that did, apparently she’s one of the best.
They believe this was some sort of developmental issue, since it was negative for mareks.