"A tomato is a vegetable."
As they say "knowledge is knowing a tomato is a fruit, wisdom is NOT using it in a fruit salad"...
Il pomodoro è davvero una bacca in agricoltura, perché cresce sulla vite, ma non voglio versare il ketchup sulle burro di arachidi.
they can be both depending on if you speak in a scientific or culinary way
You are absolutely correct in saying that it is a fruit. I would contest that it could be thought of as a vegetable in "culinary" terms. The latter, if used, really just reflects an absence of knowledge of the difference between a fruit and a vegetable. Not something those involved in things culinary would wish to be acused of I suspect.
"Knowledge is knowing the tomato is a fruit, wisdom is NOT to use it in a fruit salad..."
Wouldn't it sound more natural to say "THE tomato is a vegetable". "Il pomodoro e (sorry I don't have accent marks on my keyboard) una verdura"?