This chapter shows how far the two dorks have come over the course of the last volume or so- if this situation happened ~20 chapters or so ago Ichi would think he was doing her a favor by denying that they were close (since he was still in "she totally secretly hates me and would be ashamed if people got the idea that we were close, nevermind the increasingly gigantic mountain of evidence that she likes me" mode) and Yamada would be thrown into a spiral of insecurity over it, wondering if she was just being a burden by fluttering around him all the time. Now Ichi knows he has a chance to make this work so he's the one who gets insecure and worries that he's ruined everything while Yamada's confident enough in the strength of their bond as well as her knowledge of how Ichi's brain works that she knows if she shows how he made her feel (though obviously she plays it up a bit) that he'll do the right thing.