It's a point of private pride; Cameron considers herself to be the wronged one, and as such she won't be cruel. Never mind that her civility is cruelty of another sort, the denial of anything between them but the barest acquaintance between colleagues. If she slammed the door in his face it would be outright nastiness, and that isn't her style. Especially not now, with her anger out of its first flush. She glances from one to the other, extends a hand to accept the sandwich in his right.
I hoped you'd see my face and that you'd be reminded
"Thanks," she murmurs with a nod. It's polite.