Yeah, I wonder about that sort of thing all the time too...I don't suggest the OP raises this with them, but it makes me wonder about the definition of being a triplet.
It's probable all three foetuses were alive in the womb, but only two may have been alive outside it.
One foetus may have been aborted earlier.
Strictly, I suppose each of the surviving children is 'one of three', but I think a more common definition of a triplet would be one of three children who were all born alive, even if one didn't survive long.