I'm honestly a bit surprised at this turn. It makes sense now, cause her train of thought is clear. She's like "how can I like this little dude who's enthusiastic about manga? I'm into cool hot guys" but no, she likes him for all sorts of reasons, from their shared hobbies to the way he cheers her on to how he's got kind of a cute boy thing going but can also physically take the lead and do things like save her from falling.
But like... I thought she knew this the whole time? The beginning of the manga is full of scenes where after the two interact BOTH of them are flustered. The first volume reads like she's got a thing for him, or at least is kinda into him, from the start.
Oh well. It's a cute turn anyway, and has been handled really well. I totally buy it.