To be honest, Luke had no idea how that worked. With the speed of the enemies, he only had a few moments to hit them when they were moving and he also had to move the weapons underground in that short window… Still, it worked.
Regardless, those were overlords that have been fighting for decades, even though the weapons of their allies pierced their backs deeply, they wouldn't die yet. They also had the strength to try to pull those from their back. They succeeded with that before Luke could be free from the enemy in front of him. Still, they weren't in a condition to fight and a lot of blood gushed from their wounds. They had spirit if anything, but Luke had even more.
