Why are a group of polar bears called a celebration?

Polar bears are solitary animals, so there is not an officially recognized Word for 'herd of polar bears', just as there is no Word for 'herd of crocodiles'. In cases where other species of bears commonly live together, a group is called a 'sloth' (don't ask). Probably at some point someone just came up with the Word because of the idea that if these solitary animals gathered for some reason (which is usually the discovery of a big juicy carcass or other source of food) they look like a group celebrating something with a good meal.