I mean to be fair for both, pretty sure by now both of them already figured out each others feeling. The girl preface the confession by saying that she hates obligatory chocolates, then give a chocolate to him, she intended to indirectly confess with that, only MC didn't get it and only realized it when she calls him insensitive but in the end she doesn't outright says she loves him.
MC is the same, he doesn't outright says how he felt, but he gave her a chocolate the day after 'for demonstration'(excuse) so he could tell her his answer as soon as possible and in case that is too ambiguous for her, he added that he would give her an even better one for his response to her true love chocolate on White Day, practically already telling her that he accepts but not actually saying it outloud, just like she did. And she does realize his intention, considering the difference between her gloomy face when he says it's just demonstration and her blush when he says he'll give her another better one for White Day.
Basically, both of them are tsunderes that have trouble in outright telling the other their feeling, but despite not outright saying them, they might as well already says it and both of them knows how the others felt. Don't know why he specifically wait till White Day, but hey, to each their own.