A consciously dumb choice by the author, btw.
But, again, it makes more sense there, because Goblin Slayer isn't trying to hide the fact that he slays goblins. Presumably Lugner wouldn't want to advertise the fact that he's a liar. It's counterproductive.
And that works, for a villain that WANTS to intimidate. The terrifying warlord calling himself Bloodfist. The wicked pirate calling himself Blackheart. They're TRYING to inspire fear and obedience.
It doesn't work for a villain that wants to inspire trust and complacency to call himself Lord Liar.
That's like calling your secret evil advisor something like, oh, I dunno...Wormtongue.