Very sad that type of tragedy continues in this day.
I remember the same, "clean burning " claims misleading many people with the kerosene catalytic heaters that became popular when oil prices spiked during the late 1970's. Because of similar tragedies, within a few years they were banned in many places.
Even the oil lamps that some folks use, many seem clean burning because of using "lamp oil", but they produce CO. And even small doses of CO can become deadly because it can accumulate in our system. I have many antique oil lamps that I've converted to electric in such a way that within minutes they can be easily swapped back to oil use. But I will only use them with oil during power outages and then, only with good cross ventilation.
A buddy almost lost his wife with her doing short winter drives to night school with a leaky exhaust system in her car. She got a little dose of CO each evening on the 20 minute drive to school, another on the way home. More each day before the previous night's dose was completely out of her system. By the end of a week she was too sick to go anywhere except the Doc who caught it in time.
CO is many times more easily absorbed in our systems than oxygen. It then blocks oxygen absorption by the blood cells.