Dishonorable Kill

From WoW: IncGamers World of Warcraft Wiki

Dishonorable Kills are currently disabled in WoW's PvP Honor System. It was used to discourage the repeated killing of Quest NPCs for making questing a pain for the opposing faction. Another possible use that Blizzard has not ruled out is to "award" DKs if you kill a player of considerably lower level.

A kill did not have to be "dishonourable" to award a DK in the old system, and current "dishonourable" kills does not award DKs.