Per google: Developers are not meant to have a quit button in game at all
Google App store rejects UE4 apps with the response:
"App switches to a 2-dimensional view unexpectedly When in VR, your app should never display any 2D images. For more information and examples, please see the Daydream App Quality Requirements.
For example, your app quits into the 2D Android home screen when pressing the app's quit button in phone devices."
Also confirmed with quit enum set to 'Background'
Also confirmed when launching app from Daydream home.
Confirmed in 4.23 MAIN at CL 4961509
Result: Phone is returned to home screen
Expected: Phone returns to daydream home
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-70092 in the post.