I killed a cow and this popped up:

[Markcrow 107]

I killed a cow on my deed and a strange message popped up: Do not kill anyone but enemy players and this link. I would hate to get banned for thinning the herd. Oh, and I killed a bull a few minutes later and no message popped up. Is this to be expected or should I send this in as a bug?

 

[Evening 2,304]

That message is broadcasted from time to time and is referring to kills on pvp, for affinity farming purposes, and explained in the thread you already linked; was just a coincidence it shown when you killed the cow, nothing to worry about (other than the ghosts of the dead cattle haunting your dreams, maybe )

[Anarres 246]

Thin that herd all day long!

 

[Ayes 3,715]

pvp enemies have now adopted the tactic of hiding within cow skins. Watch them carefully before approaching and if they move slowly without mooing then leave them sneak onward in peace. Nothing to crow about really Mark but perhaps they might have some tasty insects on them from those rotting skins. I guess the smell would be a giveaway too, if only we could smell; but hey, maybe we do!

 

=Ayes=

[Wulvarik 162]

It's udderly astonishing how far some people go to farm those affinities....