It could be the tricksters at Larian are misleading us, Maybe Banes lieutenant has not been reveled. Coming to a PC near you in one week!
Or perhaps it's Gargauth himself - which would fit with the "It isn't *you* I answer to" line. Kethric is saying "my god is just as power as you are"
Gargauth's original form is a fanged and clawed humanoid with horns and jagged shards of bone jutting out of his face and back.
When manifesting for the first time to people, he wears an intricate disguise meant to convey his handsomeness and nobility, usually as a personable sage. He has appeared in the guise of a variety of races, but the Outcast only rarely appears as a female. Regardless of the species he manifests as, people almost always find him to be the most charming, amusing and knowledgeable being that they had ever met. Gargauth typically wears swash-topped boots, jerkins with slit and puffed sleeves, velvet-lined cloaks and similar finery, and usually carries huge sparkling knuckle rings, pendants, buckle ornaments, and cloak pins.
As Gargauth spends more time in one place, his true nature becomes apparent as his flesh and clothing rot and twist, horns and jagged shards erupt from his face and back, and he grows claws and fangs. By this time, though, those under his influence are usually enspelled so as to be unaware of his deadly nature.
This would explain why he looks so disheveled - perhaps the glamor is starting to fade.
Source:
https://www.thievesguild.cc/gods/god?godid=119
