I don't want to redo an argument I already had in this thread dozens of pages ago, but in that interview Arai basically said the Japanese equivalent of "I don't write yuri, I write wlw." This was then taken out of context by people who hyper-focused on the one word without knowing the history and implications the term 'yuri' has in Japanese that it doesn't in English. Regardless, Arai's Twitter profile literally says "I like love between women," and everything that she has ever written without exception contains explicitly sapphic protagonists. I don't think it's hard to guess where this comic will end up.
Also, I don't understand what you mean by "sexually confusing friendship." Like, if a man and a woman have a "sexually confusing friendship," we just call that "sexual tension." I don't see the utility in yuri fans holding a F/F relationship to such a higher standard than a het relationship before we accept it as legitimate.
Have you ever looked up a trope called "stupid sexy Flanders"? Basically, it's a thing, usually in comedy, where a character feels inexplicably attracted to someone outside of their normal orientation. These relationships don't usually end up going anywhere, even when played serious. The name comes from a scene in the Simpsons where Homer Simpson is bothered by his strange sexual attraction to Ned Flanders
While I don't, personally, think Aya and Mitsuki are straight, I was mostly pointing out why it is not unreasonable for people to feel like this story wasn't going down the yuri route if they don't know the author's previous career. Stories have done the "straight the whole time" thing before