A theoretical hazard of nuclear warheads is something triggering the conventional explosives that are used for nuclear detonation. Without the proper triggering sequence, this will NOT result in a nuclear explosion, but the conventional explosion could contaminate the local area with nuclear material.

Setting off a warhead's explosives with a simple impact is not easy. Warheads are designed for missile launches, and silo-busters are designed to hit the ground intact before going off.

I suspect that whoever got hold of the documentation in the article and wrote the story doesn't really know all that much about what they're talking about.