There's a popular theory that Kyon downplays his own intelligence in the novels. He pretends to be as average as average can be, but given his constant references that range from mythology to physics, and some comments supposedly made by the others, he's... quite a bit smarter than he lets on.
The trope being "Genius but lazy," which I'm too lazy to actually link to.
This isn't something that absurd, really, so long as Kyon is someone who has extreme rationality under pressure.
Unlike Sherlock Holmes, who relies upon almost-paranoid levels of attention to detail, eidetic memory, and an encyclopedic knowledge base, Kyon is performing common inductive reasoning on a fairly reliable set of assumptions:
1. Whenever weird shit happens, it's all Haruhi's fault. 2. Coming directly home to find someone you just parted ways with has duplicated and has arrived at your home before you when she wasn't even going to your home, anyway, qualifies as "weird shit". 3. Haruhi said some strange things, which are the best clues as to what explains the weird shit, since she's the one who's at fault.
Taking these assumptions, it wouldn't be hard for someone thinking rationally to assume that the stranger that Haruhi referred to as "Kyon" is actually Kyon.
The possibility that she once was a male.There are two Kyons.The little sister also referred to her as "Kyon-chan".Because Haruhi calls her "Kyon", and no matter how you look at it, she doesn't seem to be mistaken.Also, about what Haruhi said when I stepped into the room.Then, how can she recognize me as Kyon?If me of this world was a female for the entire time, Haruhi would not recognize me.From these facts, there is only one answer...But she became a female for some scary reason.That's the only suitable explanation to this situation, isn't it?...Whyare there are two Kyons!!but we have finally met again!She ended the biggest mystery of this world,just like that."I don't know how you changed places with Kyon, but"I don't know how you changed places with Kyon,She is the me of this world.
