This has happened to me on two series 0 watches way outside of their coverage and apple replaced them free of charge, including express mail.
The display of my Apple Watch Series 0 (original) detached. It seems the battery expanded pushing out the display.
See that’s the thing. All 3 of my Watches had no battery swelling and I was always given a Series 0 never a Series 1. Watches never had any damage either. Kind of ridiculous.