Any kind of diet change can cause gastro upset. You might want to try doing half and half for Smokey's brother instead of a total switch, then in a few days do like 75% new food and 25% old food, then hold for a few days. It might lessen the upset.
I will do that. What's unusual is he just started doing that 2 days ago. I did feed him real baked chicken and a litt ground beef as a treat when we were trying to bribe Smokey. They have never had people food before.