Yeah but Moe was talking about dating specifically. Even if they had noticed the tension between them, they probably wouldn't be talking about dating. Moe would say something like "hey, you think Risa fancies Aya" or something. Just like right before that, Moe said that about Miyu liking the kick boxing instructor "this way".
But I mean, this is what makes the most sense imo. They could still be over right after college, then Risa and Aya being just fwb during gym, then Aya getting married etc.
Recall that these are rumours, and being passed 'round by two bored twentysomethings at that. If you look at the whole business - the particular personalities involved, them being old acquaintances presumably being common enough knowledge, their charged interactions, the juiciness of the whole scenario - if anything it's slightly amazing the story making rounds hasn't already grown into something more colourful and outré than just them possibly dating...
legalize the damn same-sex marriage in Japan
It's so sad
they can't be so fucking attached to their traditions forever
Japan: hold my sake
No but seriously, that's one's enough of an uphill struggle already in "the West" where the real and figurative Middle Ages ended a bit earlier than mere ~150 years ago and there isn't a deeply ingrained cultural fetish for conformism and Confucian paternalism. And last I heard Japan is still ways ahead of mainland Asia in such matters, which probably has something to do with having been (with a certain degree of coercion) obliged to jettison a decent chunk of burdensome structural institutions and reinvent itself as something at least passing for an open-society Rechtsstaat after 1945... (S Korea and Taiwan only stopped being outright military dictatorships - a type of regime never noted for social, or any other, progressivism anywhere ever - in mid-late Eighties which AFAIK kinda shows and most of the rest of the Far East is even worse off.)