If the thing is supposed to be Nuclear (and maybe it was intended to be) then it needs to have a much bigger boom when it is used. As said above the thing is super rare in New Vegas, so it should be super powerful too as you may only ever want to use it once (like the Davey Crockett was designed to be a last ditch weapon).
"Nuclear" doesn't apply to the power of the explosive though. "Nuclear weapon" simply refers to a weapon that utilizes the energy released by atoms either through fission (utilizing highly radioactive metals such as uranium or plutonium), or through fusion (utilizing hydrogen atoms being blasted into one another and forced to form into helium atoms) in order to create an explosion.
Sure, the blast is nowhere close to what a nuclear device, even of it's size would do, but that doesn't mean it isn't nuclear. The name "mini-nuke" and "fat man", along with the iconic mushroom cloud, and the little boy modification kit stress that it's a nuclear weapon in a post-nuclear apocalypse game. It was brought in as both a humorous and awesome weapon.