In Ritsuka's defense, she's still getting used to the differences between this Waver and the one she's familiar with. So she hadn't quite gotten around to figuring out all the implications, factoring both what she already knows and the things she'd learned were different here.

That said, she does know Waver, in one form or another, and as she blinks at that reply she happens to recall how the one at Chaldea got when it came to Iskandar and--

I bet he's not going to say anything, actually.