It's much easier to make a fission reactor than a fission bomb, and much easier to make a fusion bomb than a fusion reaction. They are not even that similar.
It's way easier to make a fission bomb than a fission reactor. I reactor has to stay in the very narrow window where it's critical but not prompt critical. Even pure fission bombs can be marvels of engineering but the simplest gun-type bomb is easier to build than the simplest nuclear reactor.
Without a precisely timed neutron initiator you'll get a fizzle. Either way, gun-type bombs require highly enriched uranium. A simple reactor can be literally just brickwork of natural uranium and graphite.
Reactors are much much simpler to pull off, which is why US had the first reactor whole 2.5 years before a nuclear bomb.
Something that explodes with the force of 100 tons of TNT is still a bomb, even if it isn't a bomb as impressive as the one you were hoping for. And getting the reactor you're thinking of to the point that it worked without exploding took a lot more effort than you're suggesting.
Otherwise you just have a bomb.