mw13: It might be true. It’s still a very rude thing to say. But mik5 has no way to know it’s true. Fires happen. They exist. Sometimes accidents happen. But it’s not always due to Chillul Shabbos.
I was once at a funeral R”L of a 12-year-old who got hit by a car. Some retarded Menachem Avel, who thought it would make the bereaved father feel better to know that his child was perfect, said (I remember this close to verbatim), “Don’t think that your son did anything wrong, CH”V. The Gemara says that when a child under Bar Mitzvah dies, it’s only because of the Aveiros of the parent.” Needless to say, the Avel was not very comforted. Now, the statement might also be true, but in context it is a disgusting and retarded thing to say.