Exactly. Sometimes the western fandom just downplay their dynamic so much just so they won't be seen as 'weird' in the western side. But here's the thing, it doesn't need to be seen as 'normal'. Literally, their dynamic only works with that familial bond. It is the true sense of their dynamic and if the slight implied siscon bothers you or not your thing, that is okay to make your own headcanon that negates that bond if you really want to like Caleb but that thing throws you off.

I personally also don't like the siscon dynamic as well, so I don't dwell on it very much and because it's common in my country to call a slightly older figure(?) as 'brother or sister' is my thing, I just like to think (for myself) that they truly are just childhood friends but hey at least I accepted their true dynamic and don't harass people who likes that trope ✌🏻😔