I think Bleecker's reply is insightful. Nothing annoys me more than listening to people blather on about their digestive issues or their dislikes during a meal. I think a guest who behaves with discretion is a treasure -- to me that's far more important than whether someone eats my food.

Are these people you entertain regularly? If so, I'd ask (discreetly and privately) about the matter if a similar incident occurs. Otherwise, I would say nothing and forget about it.