"Had the bomb been armed with its fissile capsule, the immediate death toll may have reached six figures"
This statement is absolute tosh, so the rest of the article should be taken with a pinch of salt.
To detonate a nuclear device requires some complex mechanical/physical and chemical processes taking place within a very tight framework of some of the laws of physics.
If one of those processes is as little as less that a tenth of a a microsecond out of time the device will not operate.
It will explode, but only the high explosive part of it.
There will be widespread contamination and probably radiation (but no worse than Chernobyl)
But a nuclear explosion, no!