Short answers, pulled from the story.
The United States Supreme Court ruled that tomatoes are vegetables in the legal case Nix v. Hedden. This decision was made in 1893 to determine whether tomatoes should be taxed as vegetables under the Tariff Act of 1883. The justices based their ruling on common usage rather than botanical classification.
Double fertilization creates a fruit when pollen travels from the stamens to the stigma and grows a tube down the style to reach the ovary. Two sperm cells are transferred into the embryo sac to form a zygote and endosperm mother cell, which ensures the seed has a food source before it begins to grow. As the ovules develop into seeds, the ovary wall known as the pericarp begins to ripen into the fruit.
A strawberry is not a berry because the fleshy red part is the receptacle of the flower rather than the ovary. The tiny seeds on the outside of the strawberry are actually individual ovaries known as achenes attached to a common base. Botanically a berry develops from a single ovary with a fleshy pericarp that contains seeds embedded in the flesh.
Fruits ensure seed travel through mechanisms such as explosive dehiscence which flings seeds several meters or wings that catch the wind to drift miles away. Some fruits rely on water to float thousands of miles across oceans while others form symbiotic relationships with animals to deposit seeds through droppings. Seeds of nuts are often hoarded by squirrels and birds who bury them for later consumption and forget some to germinate new trees.
Fruits account for a substantial fraction of the world's agricultural output and serve as a primary source of nutrition for billions of people. The domestication of fruits has led to the creation of seedless varieties such as bananas and grapes which are triploids and cannot produce viable seeds through normal fertilization. The economic impact is immense with fruits like the apple and the pomegranate acquiring extensive cultural and symbolic meanings.