He may not be having accidents at home (I doubt that), but he must have loose BM there too. I'm sure they would like to see those clear up. Just keep telling them he has diarrhea (show them if necessary) until they acknowledge a problem, then discuss dietary changes. A Dr would advise eliminating certain foods ( ie dairy) to find the source of the problem. Even if he wasn't having accidents, he'd be spending half his day on the toilet. That's no fun for him.