And you are right to point that out, because all those senses ("horn thrust and paw slam", "domesticated vs savage") are backformations. We adopted them because they made sense.

The real origin of the terms is from the early 1700: "seller of the bear skin before the bear is caught" - old proverb - was called the player that tries to deliver goods after their price has fallen (so a seller in advance). In 1709 the term was in fact 'bearskin'.

Ten years later the "bull" was introduced as a counterpart - this time probably with relation to the images.