Totally linguistically unrelated biology smartass here: The tomato is actually a berry, and both a fruit AND a vegetable, since most vegetables are fruits. Fruits per se are fruit seed-bearing structures, so even cucumbers are fruits, despite being traditionally classified as vegetables.
Words can have subtly different meanings in different contexts. To a biologist, a tomato is a fruit, and a berry, and a vegetable, because a scientist is thinking about taxonomy. To a cook, a tomato is a vegetable, because a cook is thinking about its taste and texture, and what it will do in a meal.
Surely you will agree that 'biologically' they are fruits, ain't you? Though I surely agree that we used to call such not sweet friuts vegetables.
EU classifies carrots as fruits only because in Portugal they make a jam of carrots. To be in harmony with regulation that "a jam is made of fruits" our kids should learn a carrot is a fruit :)
Similar is with edible snails (i.e. Helix pomatia). They are classified as a freshwater fish (sic!)
World is turning upside down! :)
"So, the answer to the question is that a tomato is technically the fruit of the tomato plant, but it's used as a vegetable in cooking." https://www.lexico.com/explore/is-a-tomato-a-fruit-or-a-vegetable
No, all the nouns here are in Nominative, "warzywo" is the basic form of "vegetable". Perhaps you got it confused with plural "warzywa". If someone's name was "Warzywa", then the Vocative would be "Warzywo".
Vocative really rarely is used for something else than names, although technically the declension always exists.