They don’t understand why an egg is considered a vegetarian food. People who couldn’t quite fit in among vegetarians and non-vegetarians coined the term “Eggitarian.” But the real explanation is that caviar and fowl eggs are both vegetarian.
Animal “matter” is not present in unfertilized chicken/duck eggs (or very little). And the majority of farm eggs we eat are unfertilized.
Caviar, on the other hand, is made from the ovaries of female fish. The eggs have no possibility of being harvested if she ovulates. As a result, they are snatched from the female fish. As a result, they remain unfertilized. Because there is so little animal content in it, it becomes a “vegetarian” product.