No, the OP doesn’t take into account that adding media to Photos is not a simple “copy and store a file”. The Photos app (like all apps) has its custom Photos Library file format. So when one ads a picture or a video, the Photos app analyses it and stores all kinds of metadata that’s needed for the Photos app to work, including edit history and other bits. This is what eventually gets synced to iCloud.
If you edit a photo/video in file rather than saving as a new file, iOS retains the original file so that you can undo/revert. It doesn’t show the original anywhere in Photos or iCloud gallery. That might be the reason.
You can also edit with third party software, and they can embed whatever metadata they want to allow those edits to be modified, so there might not actually be an upper bound on how much larger you can make a photo or video by editing.
Funny, this was may take on the article too. I suppose one could download x amount of files from one cloud storage and upload it to another to see if there is any obvious discrepancy. Perhaps Apple are still using their old file system format for icloud? It's been around for a good few years now and perhaps they simply haven't bothered to ever change the type of storage format they use. Maybe those with older accounts have their images / videos on the 'older' drives?
I don't believe iCloud is a filesystem, it's not block-level. It's object-level, like S3, with a bunch of OS-side jank to make it look like a conventional directory and filesystem (which often fails miserably and dangerously).
It's similar levels of reliability to an FTP account mounted with curlftpfs[1] - except the latter at least fails in understandable ways and can be debugged.
That's exactly my mental model of it as well, some janky home made s3 fixed with tape. I really advise anybody to save their data somewhere else as well before in inevitably stops working.
If this is widespread, this could be seen as apple bloating figures to push people to upgrade, which could lead to a lawsuit, no?
IANAL