Obviously the point being that it was an angel protecting them. When our CO caught wind of that story (circa 1958) he tried real hard to track it down, and validate it. No go. Just an Urban Legend!!
When I was in primary school (hum, some years ago), I was a bit shocked to hear my Lutheran school teacher, who had been a missionary, tell the same stories to the class that we had earlier heard about JWs only.
These urban legend-type stories have not even originated with the JWs. They've been travelling around all sorts of religious groups, certainly for decades, possibly for centuries.
Faith, n. Belief without evidence in what is told by one who speaks without knowledge, of things without parallel. [Ambrose Bierce, The Devil´s Dictionary, 1911]