Yeah, I agree that it feels a lot more like Rupert/Emma than it does Ron/Hermione, especially with Emma. She doesn't have her posh Hermione accent, and both her and Rupert are mumbling a lot. But the dance scene felt a lot more like Dan/Emma than the Harry/Hermione from the books, sooo....

I think it's mostly just cause this was all improvised. Steve Kloves didn't write this scene, David Yates just thought it would be a cute idea while they were at the lake, and he spent like an hour with Rupert and Emma just filming them skipping stones. So they were thinking a lot more about what to do and what to say than to actually act like Ron and Hermione would. Still cute, one of Yates's better ideas!