I ended up here 7 years later so maybe someone else will as well. Apparently there is a way to get this from Connect IQ yourself even if you don't have any backups.
Oh god, that's a way easier way to do it!
Thanks for sharing tho, that's still a cool trick. (To be fair, the metadata URL you posted is actually one of the requests that's made when you click Edit Details, but it's still cool.)
Here's the same URL without that annoying link text abbreviation thing the forum does, for ease of copy/pasting:
https://apps.garmin.com/api/ciq-developerservices/developers/DEVELOPER_ID/apps/PUBLIC_APP_ID/metadata?isShadowApp=false
Wrapped for readability, but surrounded by square brackets (so it's harder to copy/paste):
[https://apps.garmin.com/api/ciq-developerservices/developers/DEVELOPER_ID/apps/PUBLIC_APP_ID/metadata?isShadowApp=false]