Wait, what? So it’s the same “kill” term that does 2 different thing.
I think it’s better to change Zuul’Goth’s spell to “dispel and kill” to avoid confusion.
Or… change the word to “exterminate” to continue the tradition of using every words that mean “kill” in dictionary just to fit each troops’ identities. 
The same could be asked about consistency of troop designs for specific events and regular release so we can only guess that some things are probably handled by different teams at different times with little coesion or communication sometimes.
I noticed this too, since I used to use Knight Coronet a lot. There are other, similar examples as well, I believe - Infernus/The Deep King is another (recent) example that behaves differently to how you’d expect.