Discrepancy between iCloud storage summary and actual file size in iCloud Drive

When I go to https://www.icloud.com/storage/ , it says I have 2.5 GB in "Storage". I assume that's https://www.icloud.com/iclouddrive/, right? The files there are very small - nowhere near 2.5GB. Where is the extra space?

[Re-Titled by Moderator]

Original Title: Why does iCloud storage summary show much more space in Documents than the files in https://www.icloud.com/iclouddrive/?