I can justify the jolt apart by simple surprise — Vivio really did make a lot of sudden noise in coming in. Really, though, for this reading, they're both kind of reserved, and put a certain amount of effort into seeming in control. It's the same sort of thing as the Vivid Life chapter in which they've been lazing around all day in their pajamas, but when Vivio comes home they're suddenly in Barrier Jackets and playing mock battle, to keep up the adult facade.
(They're still quite young to have a tween. Vivio has Kris, so it's Vivid era, so they're, what, 23?)
