Kiaane just blinks, which means they don't know.

Kiaane starts to shake their head but pauses as soon as the second question is voiced, possibly because whenever there's more than one question asked in their direction, their mind automatically short-circuits. "Dinner?" they ask like they don't know what it is.
Yep. Their mind definitely short-circuited.

Kiaane shakes their head. That's a no, mostly because they don't eat dinner unless called. 

Instead of responding immediately, the mercenary just studies Martin. Their gaze, as usual, is rather bellicose, but even if the eyes are supposedly the mirror for the soul, one should still not judge another for their eyes.
"Another sandwich can be made 'later,'" they respond. "Food is best served fresh. 'Healthier' that way."
By the way, by 'made later,' they mean they can make one for him later if he wants. It's not so clear how they say it, though. 

Kiaane points vaguely at the ceiling. By "vaguely," one means that they didn't even finish the part of pointing where you actually isolate the one finger--it's more like they just flopped their hand backwards. "Eating dinner is also healthy," they...lecture? It could hardly be called that, but that is the intention.

Yay, and Kiaane's not going to convince him. That ain't their job. 
The cricket's somewhere inside the sleeve. Maybe it's asleep, since it hasn't chirped at all.

Instead of going "I don't know" like a normal person, Kiaane instead just goes completely motionless and silent as they listen for impending footsteps, verbal intent to enter the kitchen, or anything of the sort. Best of all, after a bit, they apparently presume Martin also did the same thing as them, because they don't even elaborate on their conclusion, which is "No." 

"No," they repeat, though it could very well be taken the wrong way.

The entire time Martin's head is rotating around, Kiaane is just staring somewhat attentively at him. And then that slight upward tilt of their head is supposed to be the equivalent of a nod, which means they are indeed planning on going outside again, though the specific detail there is that they plan to do it later--which they don't indicate by a mere motion of their head. 

Another strange nod on their end. But this time, they add a "Why?" as in "Why do you wish to stay here?", not "Why does that mean we can stay here for longer?" 

The mercenary pauses a bit when he repeats what they say, but it doesn't seem to provoke a large reaction from them. They just keep standing there, their hand held tightly around the sandwich like it's a disobedient animal with legs instead of an inanimate type of food. And since he didn't say much that could warrant a response, at least from them, they just kind of soak in what he has said like a sponge. A very antisocial sponge, apparently. 
Maybe they should ask why he doesn't get to be in here a lot, or maybe they should even consider that themselves, but they're probably not doing either of those things.

It takes a while, but then they ask, "How long?"

"Shouldn't," Kiaane agrees.

"Then why stay here?" Kiaane turns their head to stare off absentmindedly, trying and failing to think of places with sticks.

Well, at least he knows they carried a stick with them before, so maybe? It would imply that they don't necessarily dislike sticks.
They're actually confused now. (The only indication is that one of their eyebrows is scrunched up a little tighter than before.) Earlier they had presumed that he was here because he didn't get to be in here often, but now he's explaining it to them being here. Technically, that wouldn't be so hard to understand, either, but technically, Kiaane isn't all that intent on being here and are only here because Martin is. Kiaane's mind doesn't work all that well in the first place, but when it comes to paradoxes and contradictions, it only gets worse from there.
Also, somehow they're failing of thinking of places with sticks. Yay!
Anyways, the only other indication of their confusion is that they're completely still, but that also needs an "again" added to the end of it, which means it's pretty hard to see why they're suddenly just standing there without responding all of a sudden. Don't worry, they're about to arrive at a conclusion. Just...give them a bit, and preferrably add some undistracting verbal filler.