Flu does not necessarily imply gastro symptoms. Influenza A and B may cause gastro symptoms in children but rarely in adults. Rhinovirus is a cold virus that can potentially cause diarrhea and is transmitted by the oral/fecal route. “Stomach flu” is usually caused by rotovirus or norovirus which are not that closely related to influenza A,B, or C. I dont have any problem calling any of these flu.