No, it's cooler than that! All these vegetables are cultivars of the same species (Brassica oleracea). Citrus trees are different species with common origins.
If you think that’s amazing - look up what bananas looked like before human cultivation. Basically any fruit or vegetable you eat is the product of centuries of humans carefully selecting what seeds to save and plant.
My wife and I had fried plantains at a Venezuelan restaurant a couple weeks ago. That shit was absolutely divine with beans, rice, meat, and a fried egg on top.
Just like dog breeds look very distinct, but cranked up to eleven with horrible deformities. Imagine if we continued to breed chihuahuas to have bigger heads and smaller bodies until they are 90% head. Or breed a breed of hound to be smaller with increasingly bigger ears until it's 90% ears. They would still be dogs of the same species because they can procreate together.