2 things. We had a BBB tom that appeared to fall off his roost and break his neck when he was about 4 months old. Perhaps he was startled. He was a big old boy, too, so I can see parts of it.
Second thing. I have ALWAYS raised my turkeys and chickens together. For years, and have never had any problems with diseases or fighting or anything. Couldnt say for sure if they actually passed immunity to each other or not. But think about this. You have to have black head disease to start with in order for one of them to pass it to the other. I obviously dont have it, and am told that it is rather rare in this part of Missouri. And yes, all my birds came from the hatchery as day old chicks that we got at the same time. The only exception would be the 8 hens we kept over from last year. Even had several guinea hens with them. And this year I have 2 Emden geese as well, and they all get along fine.