Do boomerangs really come back?

Some do and some don't. It all depends on if it was designed to come back.

The original purpose of boomerangs was to simply injure prey and stop them in their tracks. Returning boomerangs were largely used for herding animals into traps, or killing birds, and they had to be thrown with the correct technique - they did not just automatically return. Other boomerangs were used as tools for clearing ground, a shovel in cooking, digging holes, and even carving up a cooked animal.