Some yall motherfuckers never been bullied if ya aint see the kids point of view.
He yelled at her. He didn't throw her out the window or anything. That is not an extreme reaction for years if bullying. It's the first step.
But he wasn't being bullied when he actually decided to snap, which is the "strange" part.
The point is that the two of them had completely different perspectives on her actions, and she got blindsided by the consequences of her actions because
she never viewed her behavior as discontinuous. What's odd for me is that someone in that situation would be more likely to be utterly bewildered or suspicious by this discontinuity regardless of whether they'd still reject her-- but he isn't. He isn't acknowledging that she, specifically in that moment, has done nothing wrong and went through the effort of bringing him dinner. He went as far as to make an assumption that's wholly contradictory to her actions and words in that scene.
I wouldn't expect much conversational depth from a manga in this format. Even the characterization and general narrative is shaky, if you take it more seriously than you should. The heart of the manga is seeing mesugaki being emotionally crushed as a response to their actions. But this isn't the first chapter where the chapter's heroine is cast in a vaguely sympathetic light on account of the reaction not fitting the situation or the mesugaki getting disproportionate blowback.