Maybe the confusions was your use of the term “hybrid species” instead of “hybrid offspring”. A mule is not a “hybrid species”.
I think it went like this: the people who first came across a wapiti in the forests of North America had never actually seen an elk, they had only heard about them, so when they came across a big deer they assumed it was the same kind of animal. When other (or the same) explorers met a real elk the name was already taken, so they used a local name for the animal.
That is a peculiarity for the English language. All other Germanic languages (at least those I have checked) call all “Cetacea” whales, regardless if they have teeth or baleens.
That’s not really the issue. In English, we distinguish between the larger toothed whales and the smaller ones. The latter being called dolphins or porpoises. We don’t have a non-scientific term to distinguish between baleen and toothed whales. Just big and small.
A non-biologist, non-whaling Norwegian will separate “whales” and “dolphins” and put baleen and large, toothed whales in “whales”.