Тъй като на днешната форумна не можахме да стигнем до окончателен отговор, се поразрових и намерих това:
The answer to this question is actually a bit complicated, thanks to some disagreements among botanists about the term “vegetable” and the efforts of the grocery industry, which have further clouded the difference between fruits and vegetables. Simply put, a fruit is the ovary of a plant, which means that it may contain seeds, while a vegetable is a plant part, which does not contain seeds, although some vegetables may be used in plant reproduction.
Some examples of fruits include well-known specimens like apricots, cherries, blueberries, and apples, but tomatoes, pumpkins, cucumbers, and zucchini are also considered to be fruits botanically, even though many people refer to these fruits as “vegetables” because they are savory, rather than sweet. This is the result of convenience labeling used in the grocery industry, where fruits and vegetables are differentiated on the basis of whether they are sweet or savory, rather than with the use of any firm botanical criteria.
A vegetable, on the other hand, is simply a plant part like a flower, stem, root, or leaf. Broccoli, for example is a vegetable which appears in the form of a flower, while celery is a stalk vegetable, and celeriac is a root vegetable. Vegetables like potatoes are technically tubers, not roots, meaning that they are specially designed plant structures which store nutrients for the parent plant; tubers are also capable of budding into new plants. Some examples of leaf vegetables include spinach, cabbage, and lettuce (от wisegeek.com).
С други думи разковничето е в семената, а не в захарта
. А объркването идва от това, че някои си използват наименованията от ботаническа гледна точка, а други - от кулинарна 
А динята според горното и според wikipedia е плод
