Now, I shall no reach for my torch and pitchfork just yet. The writing so far has been pretty solid, so there is a chance the author won't resort to one of the most annoying tropes to ever exist (while adding another layer of retardery).
Because let's be real, there is no logical way Nine could get the impression her reaction is in response to him. Imagine it. You are talking to someone, they move their focus of vision from your face to something behind you and make a disgusted face. No matter how unsure of yourself you are, you will not assume that the reaction is to anything you just said. And at this distance it is impossible to not notice that she isn't looking at his face any more.