I know the answer probably gonna be something like "oh she's just really immature or w/e," but she doesn't read as autistic to me, she reads as asexual. Might be me projecting 'cause I rarely see any ace rep anywhere (and tbh Chita has been nothing but annoying, but something's better that nothing I guess?).
(I abridged your post since I'm not referring to any specific points, just wanted to not accidentally delete the reply box)
It's not necesarilly autism, but does read as some sort of developmental issue rather than just being aro or ace. I've got a pretty wide-ranging group of friends in terms of both romantic/sexual preferences and (i hate the words but lack an alternative here) neurotypical/neurodivergence.
One of my friends is aro/ace but not autistic, and from past conversations she does broadly understand the whole romance and sexuality thing despite not experiencing them herself.
By contrast, when I described Chii's current situation to a friend of mine who is ace and autistic (but not aromantic - she has a boyfriend), she referred to Chita as a mood, having similarly a (albeit less severely) stunted ability to understand those things.
Regardless of the root cause, though, it's fairly clear that Chii is dealing with a lot more than just "I don't feel non-platonic attraction", nor is she really showing tsundere behavior which is more characterized by an unwillingness or inability to accept her own feelings towards someone. Instead, she's struggling with not understanding other people's feelings - both those directed towards her, and from seeing her friends who are engaged in more "adult" relationships.
The author is pretty clearly aware of general romcom tropes (hard not to be after 200+ chapters), but Chii isn't really falling into the typical behaviors if they were going for a tsundere type of thing. Instead, as her internal monologue shows in this chapter, she doesn't understand how (and/or why) other people have those sorts of feelings - in addition to not really experiencing them herself.
BUT, we're still looking at fictionland, so her having a big mental breakthrough which isn't really possible IRL is very much on the table.
