Returning boomerangs were unlikely to have been used as weapons.

Not really. https://en.m.wikipedia.org/wiki/Boomerang

  Although traditionally thought of as Australian, boomerangs have been found also in ancient Europe, Egypt, and North America. There is evidence of the use of non-returning boomerangs by the Native Americans of California and Arizona, and inhabitants of South India for killing birds and rabbits.

Hunting boomerangs didn't return to the thrower. Picture a symmetrical returning boomerang you're used to, now massively shorten one of the "legs": that's the hunting boomerang I've been shown

To be a bit more specific returning boomerangs were used to hunt birds. While the non returning boomerangs you refer to were used for land animals and warfare.