Goblin Slayer is very disappointed in you MC, for not being able to clearly understand this basic distraction tactic thought up by a goblin. That's what happens when you underestimate them and think they would just simply come fight bravely in a frontal assault. Goblins are far too cowardly to do that, but a bunch of them could easily be fooled into thinking they would be safe by a goblin lord who would take the opportunity to attack from the unguarded back and be the first to get his hands on the women for his own desires.