Uninstalled Google Photos before turning on iCloud Optimize Storage, now it says 7k items to backup. Am I getting duplicates/overwrriten with low quality?

Hey everyone,

I messed up the order of operations and now I'm panicking a little.

What I did:

1. I uninstalled the Google Photos app from my iPhone (at this point, my entire camera roll was already fully backed up to Google).
2. After uninstalling, I turned on iCloud Optimize Storage to free up space, and iOS started shrinking my local files into thumbnails.
3. I just reinstalled Google Photos, turned backup back on, and now the queue says it has 7,000 new items to backup. It looks like it's scanning through all my old stuff.

My question: Is Google Photos actually going to re-upload all 7k photos and create massive duplicates in my cloud or will it overwrite photos with low quality? Or is it just "scanning" the library to realize it already has them?

Because I uninstalled the app first, did it lose its local database memory of what was already backed up? If you've been through this specific headache, please let me know what happened to your library