It seems my wording for that sentence was shit. Iirc basically Izumi tells him that they already did stuff together before, you know back in chapter 12.2 and that went well. He gets a bit too into it and has to point out that it wasn't planned. Right, they met by chance and all that. He makes clear that is wasn't an actual date or meetup or anything really. Chronologically the chapter is happening before the first one and they aren't a couple there either (well, yet).