The hero was not wrong when he said that there was something that chipped at Rude's shell. It's because Rude has Shield of Sacrifice, a Super Super Rare skill compared to his Provocation skill, which was only Rare. It takes damage from party members and gives it to Rude. The hero never got hurt, because Rude's been taking the entire party's damage. So when the hero gets hit for 20 damage, it's Rude's hull that gets hit with 20 damage while the hero gets no damage.