Here is my opinion on the subject. If he is a "dog food dog", then any change in his stool after eating people food is caused from enteritis. Dogs that only eat dog food are very sensitive to people food especially greasy food. Don't feed him anything for 12-24 hours and let him get it out of his system, then feed him a bland chicken and white rice diet. then add his dog food back into it. If you do take him to the Vet, take the stool with you.
If the stool is fatty or frothy, it's going to be enteritis from the greasy people food. Tell brother to Stop feeding your dog or her will pay the vet fee.
The Pumpkin is good for diarrhea.