I am sorry your piglet died. It is always sad. It is possible it ate something that hurt it's insides. I remember a piglet we lost back in the 1960's. My dad cut it open to see what caused it because there was nothing on the outside. It had swallows a piece of stick about 5 inches long and it had punctured it's intestine. It bled into it's belly.

I hope yours did not die from a virus or bacteria that the others could catch.