CloudDocs > session folder filled with version of a Pages file
I don't know the answer to your question, but I have the same folder which is also huge. I'm pretty sure they are indeed incremental files.
I have a few different ones, but there's not one for every Pages file I own, which makes me believe they are the files I wanted to "revert". There's an option in Pages, Preview, Keynote, Numbers and more Apple applications that lets you revert to a previous version. I think what happened is that it saved all previous versions.

I just opened some of those files and tried to revert them, but they don't even revert back to all of those saves! Those gigabytes of files are there but I can't open them and I can't revert to them.
I deleted all of the versions of one document and opened the actual one, the document was still complete.
I did the same with another and the actual document is fine. I think you might be able to delete all of it. Maybe make a backup before you do so if it's an important file.