Two things have occurred to me:
1. CW saying that NK was the first person he could be himself around. I think this might be true. Around SW he had to wear his mask, because she was truly and innately a good and honest person with a fully functional moral compass. If he were to have revealed his abject emptiness (i.e., his sociopathy) to her, she would have rejected him.
CW required, as a nearly literal matter of life and death, the approval of others, so he learned to wear his mask religiously, as it were, when in the company of good and decent people. His family of origin is excepted from this equation because he needs their approval despite their lacking in the decency department - so he wears his mask, to one degree or another, with everyone.
Except NK. Because she was like him. They wondered if they were "bad people." IMO, this was an honest question on both their parts, because they have no concept of what being a good person is beyond the outward clues they've gleaned from their observation of others.
2. CW wanting to be a mentor and/or his feeling that he has a purpose or whatever nonsense he said. I do not think that this is something he truly feels. Has he ever had an authentic and genuine feeling in his life?
More likely, IMO, this is more evidence of his compulsion to appear "good" in the eyes of others. Somewhere along the line he has absorbed the notion that people think well of those people who desire to help others regardless of their own station in life, and/or people who make something good happen after, or out of, terrible times.
He no doubt heard, at some point in his life, someone else expressing such a sentiment, and then heard as well the attendant approval-sounds and murmurings. As he dearly desires such affirmations for himself, he likely pulled this out of his memory banks (where it was doubtless filed under "save this info - may need one day") after spending 23 hours alone in his cell every day trying to figure out if he is "bad," if "everyone" hates him now, and if so, how he can change everyone's mind the way he's seemingly been able to do every other time the mask has slipped before.
CW is just polishing his battered mask with whatever he can find lying around his "how to act like a human being" memory files.
All MOO.