I believe the "droul" as they call it on the wiki has no tier 3 form and instead you see it in its tier 2 form down in the tier 3 depths.
Unlike all the other variations of the dust zombie, the droul is the only one without spiked shoulder pads and small spikes to go on top of the skull.
He should be replaced with a more menacing version of himself in the tier 3 for the sake of eliminating the error. Who wouldn't want to see a cooler version anyway?
Yes. T3 poison zombies always looked so scrawny.