I don't think it's really Airi's interest in Shingo that's up for dispute - she is quite interested (attached?) in him in a lot of ways, even if she hasn't consciously caught on to her inner feelings just yet. Rather, it's whether Shingo has displayed actions that would translate in to romantic inclinations towards Airi from his end.
There is no doubt his relationship with Airi has the most solid grounding at this point, due to all the interactions and coming to understand one another in context of the previous episodes, but I don't really think he is looking at her in romantic light just yet. A newfound and good friend, someone he is glad to have on friendly terms with him, yes. But a prospect for romance ? I don't get the feeling said thought has crossed his mind just yet. The solid grounding of their relationship could certainly serve as the basis for one, but the spark doesn't seem to be there at the moment.
In contrast, it's not hard to spot the implications of his appreciation for Miu going beyond that of a good friend. While the groundwork of their relationship as of yet isn't nearly as deep as what he shares with Airi, there is little doubt she has caught the attention of the "male" part of his brain
Don't get me wrong, Airi is certainly a distinct possibility and it wouldn't be hard to develop their current relationship in to a romantic one, but I wouldn't write Miu out just yet (as that's where his current romantic inclinations point), contrary to what I thought a few weeks ago. His relationship with Miu is lacking the same depth as he shares with Airi, but judging from the preview the "club" surrounding events aren't over yet. I suspect the next 1-2 episodes should shed a lot of light in terms of their final destination (I'm fine with either choice, they are both adorable in their own way), so am awaiting those with anxiety.