When Gaila calls for the lights and asks if Kirk doesn't love her, too, Kirk sits back and says, "No, I meant..." -- correcting her, as though he was meaning something else completely. Then Uhura interrupts them.
He's not talking about what she said.
I've only watched it once, but is there any chance what he's actually reacting to is Uhura returning?
No, because he was surprised to see Uhura. It is not impossible that Uhura made a noise prior to entering the room, a noise to which Kirk was reacting, but it's an implausible explanation because we don't hear it.