What is highly unusual about this find is the perpetrators (winners) went to all the trouble to bury the victims.
Most biblical massacres talk about leaving the victims to be consumed by wild beasts and birds of prey.
Definitely a lot of labor; ultimately there's no way to know who buried them. Survivors may have come out of hiding (or returned home from a hunt) after the perps left and gave them the only form of burial they could manage.
It does not make much sense. Maybe these were the remains of their own, killed by others.