He looked younger than his seventeen years, but she knew this was partly deliberate, to lull people into a sense of- not trust - but comfort.
I'm thinking, maybe, -
a sense of - not trust, but comfort.
I like the broken feeling of the language here -- the second, I agree, reads as a little different from the first. I'd read it as a break in thought, a sort of small interruption to the flow.
I read it as:
'... to lull people into a sense of -- not trust [there's a silent 'exactly' for me about here], but comfort.'