This is simply a restatement of the weirdness. Yes, Shima did not literally say, “I love women to the total exclusion of men,” but the presentation of her coming-out scene strongly suggested just that, and, until this latest chapter, readers had every reason to believe that Ise understood it that way, without any need for further clarification or discussion.
Any number of other manga have contained scenes with some variation of “I fall in love with both men and women/ I thought I was straight until I met so-and-so/ gender doesn’t matter to me, it’s the person I love,” etc., and Shima’s revelation was nothing like that—it was a classic, “I love women, I’ve suffered socially for it, and you must think I’m disgusting and twisted” lesbian coming-out story.
Yes, in the event this chapter does suggest that Ise must have been incredibly dense or oblivious to what Shima told her in Chapter 15, but until now there was absolutely no reason to suspect that was the case.
I think there's a couple things to it. First, Ise knows for sure Shima is into women, but she may not actually know with certainty that she isn't into men, and she might have just wanted to confirm that before shutting him down. I mean, part of bi erasure is the fact that people tend to just assume that if we like the same sex we're gay, and if we like the opposite sex we're straight, but the truth is, if you haven't specified, then you haven't specified, and it could actually be considerate for Ise to entertain that possibility before turning down what might be Shima's great destined lifelong romance.
(I mean, she has not yet realized that she IS Shima's great destined lifelong romance, after all.)
We don't see her thought process, and we don't actually know what she told the guy when he asked. If I was gonna guess, I'd assume it was something like "Ummmm....I'll ask her, I guess."
Secondly, even if Shima is 100% definitely no holds barred supergay ladysexual, it's not like Ise can use that as an excuse to turn him down. She can still turn him down, but if he asks "Why not" she might not have an excuse at the ready, especially when he put her on the spot unexpectedly.
So when she goes to talk to Shima, Ise comes at her with this weird, kind of vague question, because she's trying to get a solid idea of whether Shima is gay or bi, and if it's the latter, what her tastes are, but ultimately, she's just trying to pass the buck on shooting the guy down.
And then of course Shima gets pissed, because that forces her to be the bad guy, and because she's sick of her friends trying to hook her up with guys. (Also probably secretly because she's upset that Ise is fine with her dating somebody else.)
Basically I think Ise is just being conflict avoidant. She wasn't trying to actually set them up, just get out from under an awkward request. (Which, to his credit, he recognized when she finally did turn him down. It was kind of shitty for him to ask Ise instead of just confessing directly to Shima.)
As for whether Shima actually is gay or bi, I think it's not ironclad, but she's probably gay. She didn't give any indication of being into guys when she first came out to Ise, that's true, but also her concern at the time was that Ise would be disgusted to live with someone that is into girls at all. Since the attraction to women is the source of potential conflict there, it'd make sense that she'd focus on that aspect rather than clarifying the full range of her sexual preferences.
(I mean also I'm pretty sure she was more worried about it because she was specifically crushing on Ise herself. But the point stands.)
All the other times she's talked about romance, it's been in general, non-gender specific terms. She -did- say in this episode that her tastes go "regardless of gender", but as Ise noticed, her language was vague enough that she might not have realized Ise was asking about romance. And the fact that she didn't like it when her friends set her up with guys might be because she wasn't interested in any of them and didn't like being put on the spot to have to reject them.
