My favorite idea is that Hiyori has no idea what he's talking about when it comes to everyone's relationships unless it's directly stated, but he's very good at clocking when someone has a crush on someone else (unless the crush is him but whatever). I think Hiyori clocking that Makoto has a crush on Haru and assuming that they're dating would be funny bc it cements how he really doesn't know these guys and also how his own bias (his crush on Ikuya and aligning the situation between their relationships to each other) impacts how he views them.
Anyway, Hiyori meets Rin and clocks his crush on Haru, and like Hiyori, he feels bad bc he thinks Haru is taken and tries to help Rin move on by setting him up with other ppl (Hiyori is also trying to move on). Haru is in the back trying to explode Hiyori and everyone else assumes that Hiyori is just doing this to be a brat to Haru, except Ikuya, who thinks Hiyori has a crush on Rin.
