It was hard to process what happened, but while I was being chased by a Grimalkin, a mewkat spawned and got caught by the Grimalkin's bite. It died, then dropped a Ghostly Aura. The wiki page didn't mention Mewkats dropping anything as valuable as an aura.
Link to Kat wiki: http://wiki.spiralknights.com/Kat
Proof of Ghostly Aura: http://steamcommunity.com/sharedfiles/filedetails/?id=318628103
(check the drops received on the bottom left)
So maybe there is an incentive in killing these adorable kats...
It's hard to tell from the transcript, when that drop happened. You're sure that it didn't drop from a treasure box that you opened?
(I have no particular reason to doubt you. I'm just trying to make sure that only accurate information enters the wiki.)