Okay I know how the last page seems kinda messed up from our perspective, but if we took Kagiura's perspective into consideration, he might think what is he doing is a "logical" outcome.
So I'm pretty sure Hirano never out right said to Kagi that he doesn't want to do kisses and stuff, he only asked Kagi if he would want to kiss him and that's it, so maybe Kagiura thought that question meant that Hirano was implying that he is interested in kissing, and then right after the festival ended he says that he has an answer to his confession with a flushed face. With that in mind, I think it's easy to see why he ended up thinking this outcome is only natural.
(of course that doesn’t excuse what he did and he should’ve let poor Hirano continue the confession we waited YEARS for, or maybe Kagiura didn't actually kiss him and Harusono is playing tricks on us like the others mentioned lol)