That really sucks! Sorry for your loss. I had a frog throw up his stomach once, I caught wild northern leopard frog as a kid and taking it home it did that. It soon passed, I was pretty upset. I am sure it was stress that did it in.

If you raised all of them in a similar manner i would be inclined to believe that this was out of your hands. A possible genetic defect? some weird illness/infection? possibly causing enough stress to the guy that lead to him expelling his innards.

Hopefully someone else can shed some more light.