You’re right! It is a spear thrower! It is sometimes called a propulser.
The spear thrower would have been attached to a bit of wood to make it longer, and the hook made by one of the woodpeckers on the poo/baby would be lodged in the end of a spear. The hunter would then be able to throw the spear much further than if he or she just used their arm and hand.
The record for a modern person using a spear thrower today is 260 metres. You try throwing a spear with just your arm and hand and measure how far you can throw it!