Were his both eyes black, it would have been a very bad sign, even in Kell's home. One just marks him as Antari. He's so used to people flinching at his eye that he barely notices Castiel's reaction.

Both, the black and the blue, go wider when Castiel introduces himself.

"He said you would be looking for us" Kell says, surprise very obvious in his voice.

It's less that he didn't believe in Lucifer's promise, and more because the last time people were looking for Kell, it was to accuse him and eventually to arrest him... not look after his well-being. He's mostly used to other people assuming he'll be fine. He usually is. This is an exception.

"Mostly in my wounded pride that they were able to grab me from the street just like that."

His reply is humorous, but Kell's hand goes to the back of his head, where the bruise from his initial encounter with the Acolytes still refuses to heal. He just doesn't think it's worth mentioning. Other people got it worse. He's wrong about that.