She's not confused why he dislikes her, she's wondering why he seems to hate her to increasingly irrational degrees with every encounter even when she has not been actively doing things to worsen his impression of her.
While it is hypocrisy, i 100% agree with you on that (and, for the record, im not defending him since he's a character im not particularly super happy how he's being handled) I haven't really seen a person who's close family member was murdered have a level headed hatred for someone. If i remember correctly, for all he knows she's the reason why his grandmother died and thanks to the fact she decided to take the mantle as the villainess, it's not exactly logical but for someone who was already actively fighting the idea that Iana is the worst of the worst, i'm not exactly surprised.
I would imagine a high schooler would understand the fact that giving someone good reasons to think you're the worst of the worst, they'll take the chance to blame you for everything if you're even mildly involved.
Do i think there's a hot chance that we're not being told everything, and (this is my own guess) there could be someone we're not being told exists feeding him lies to make him hate her to an obsesive level? Maybe. But i've been struggling to remain interested since it's relying too hard into the fact this is a high schooler's self insert story to consistently destroy any level of tension (I mean, come on, you'd imagine after 70+ episodes she wouldn't react the same way she did at chapter 1)