Draco was shocked to find that the Green Orcs were still locked in battle with parasitic monsters. He had been certain that King's death should've ended the main storyline for this Unique Quest, but it was clear that he had been wrong.
Draco assumed that King had shown that flash of hatred due to him mentioning that he would kill all parasites but…
It was obvious that this was not the reason.
After all, the real reason was that Draco's aura had put pressure on King, making him feel fear. As such, King's pride made him feel hatred for Draco because he had created such feelings of fear in him.
King hadn't cared about the comment about the parasitic monsters, but the timing had been too good, between the display of his hatred and Draco's surmising. As such, it had created this false assumption.