This is interesting...Why does it feel when Moeko shouted out "I KNOWWWW" that she was bottling up her feelings. as if she likes him or something? Yeah and at this point she knows about him and Anna. But when? I am curious when did she discover that and how she feels about it. it almost feels like shes envious.
There's an extra covering some of their grade-school days where Moe pretends that they never had any real interactions or even shared a classroom back then, both of which Icchi burns down thoroughly. Given their academic rivalry in middle school, that also almost certainly extended back into at least their latter elementary years. He was helpful. He was a pain. He was just always kinda...there.
(My own head canon holds without any doubt that she was thrilled to take the lead on their rivalry as first-years and pissed that she only did so by two positions despite Kyo basically being a dead man walking that entire year. You're perfectly free to dismiss this entirely, of course.)
All this to say that her feelings toward our boy have been all over the place for a long time, going back at least to the Line business where she recognized the mutual attraction between our MCs, shooed Yamada off toward the track dude, randomly dropped a casual insult toward Ichikawa and then got his ID for herself. None of which actually went anywhere for her.
My guess here is that she crystallized all of the lingering Icchi mess in her head into that simple "because we're friends" statement. Not that she's gonna be above indulging herself once or twice (wait for it), even so.