Beavers also use castoreum to mark their territory, for the record. There seems to be some history of using mammal scent glands for perfumes…people have also used musk from musk deer, which have needed to be protected because of it, and perineal secretions from civets, which are farmed for them. It seems disgusting to me but I guess you can imagine people thinking that if the smell is attractive to the animals, it will work for them too? Anyway I think this probably started there, and people realized it could be flavoring too later on.
