Come on, people. They are small enough to fit in a suitcase, not the size of a huge truck. The metallic cylinder attached to the bomb (implosion device) was like straight out of a James Bond movie. The detonation itself: the blinding light, the blast blowing first out, then the air coming back in, and lastly the mushroom cloud. They are all textbook nuclear weapon descriptions. We even had a lake of lava as a bonus... We saw the whatever international assembly scene trying to ban the weapons. Whenever would nations try to ban ordinary explosives? Not that there would be ordinary weapons able to destroy a whole town.
So, unless HxH has a new branch of physics in addition to the nen powers, this was a nuclear weapon of the simple linear implosion kind since it was called cheap.
The only time nukes have been used in a war in our world certainly showed the user is not interested in reclaiming the freed space. A terrorist also wouldn't be interested in it, since a terrorist is only interested in generating terror in their enemies, like the name implies.