@Mikainox Well to be fair, it's one of the few times he does get one over her (even if he didn't mean to or even knows about it) as opposed to her relentlessly teasing him whenever she finds something secretive about him. He's not exactly a jerk as much as he's just insensitive (and even then, she doesn't exactly make her feelings clear to him with the teasing and stuff), so he can't really be blamed all that much.
If anything, if they did go on a date for her birthday, I can see three different ways it can play out:
1) She'd find something super secretive about him, tease him about it the entire time and call it the best birthday wish.
2) She's sincere about spending her birthday with him, but because of her constant playful nature and the possibility of the first scenario happening, he makes the assumption that she's going to make fun of him in some way, causing her to get upset and run off, him feeling like a jackass, and then apologizing and making up after a talk.
3) No shenanigans are in play, and it's a wholesome chapter that opens his eyes to how nice she can be when she's not teasing him.