No, I mean because the writer of the article was either stupid, or made things up.
If the bomb was going to explode on accident, it would have been from the shock of hitting the ground. That clearly means it wouldn't be "over" the land, city, or what ever. For maximum effect, these bombs are designed to trigger in the air, above their target.
I simply cannot stand to read BS from sites like the guardian, common dreams, etc. because of this complete lack of professional journalism. The mainstream journalists are bad enough, but these whacho sites seriously cross ethical lines of honesty regularly.
Now...
If the switch had manages to somehow short on impact as well, and the detonation explosive went off, it still would not have been a nuclear explosion. That same impact would have misaligned detonation explosives, which must go off precisely to compress the sub-critical mass to a critical mass. Chances are, the core would still remain intact, and at worse, it would have been a dirty bomb. Not a megaton range explosion.