That stinks. Are you sure it was the rice milk or could it be something else? It just seems so odd that would bother him.
It also sounds like maybe he is more than just lactose intolerant with the cow's milk, he may have problems with the milk protein.
They told me Matthew would likely outgrow his milk allergy (apparently lots of kids do by age 2, including Matthew's cousin) but I don't see it happening either. His pedi told me at his last appt that if he outgrows it, he will probably be one of the kids that outgrows it at a later age (maybe by age 4???) since he still reacts so strongly to milk products (diarrhea with mucus).