Just gonna toss this out there, but what if Hina said what she said to throw off her "ex"?
Like, she knows that her "ex" has the Yurihots for her, but she's only got eyes for Hana, so in order to keep the complications to a minimum, she announces that she's totally hetero omg, with the idea of running off the "ex".
NOT REALIZING OF COURSE that she's shooting down Hana-san as well.
I mean, I dunno if this is how it's going to play out, but it'd be pretty neat if it did.
Also: I think the ex really was being set up to be a legit ex, but Morinaga had to switch boats mid-stream after the cancellation announcement came. The whole explanation about why she's called her "ex" just rang like a tacked-on retcon to me.