Time machine restore iCloud Drive
iCloud needs to check that the restore from backup is the same as the current state on iCloud Drive, so it's not uploading the entire file where it already exists on iCloud Drive but instead just comparing hashes.
This process should be much faster than re-uploading the entire iCloud Drive contents. The progress reported by Finder (in GB) is the size of the files that still need to be checked, not the amount that will be transmitted over the network.
This will also happen in other circumstances where iCloud loses track of the local copy of the drive, such as after a logout of iCloud.