When the passenger side is in SYNC, it means that it's in sync with whatever temperature you have on the driver side. When you click to reveal it like you described, you're actually disabling the sync.
Sorry if I’m misunderstanding here, but you don’t need to reveal the passenger temperature, with Sync enabled it will always be the same as the drivers temperature.
All they have introduced here is a GUI change.
I'm not sure how it was before, since my Golf came with 1804 and on that version it already said SYNC, but my guess is it was to make it clearer for the user that SYNC is active without having to bring up the climate control menu.