I was at the start of CoE, where you fight the Icebrood Elementals and Icebrood Goliath. I hadn’t killed the wolves yet, but at the time when the elementals and goliath died, I got the Ogre Slayer achievement.
I would have expected them to count as Ice Brood, or even Inquest, since it was an inquest themed dungeon.
P.S. There should be a way for us to identify what “race” the enemies count as, to make these Potion of x Slaying and Sigil of x Slaying a little more practical.