I tried to find files authored by someone other than bzimport at https://bugzillapreview.wmflabs.org/file/query/all/ but I could not find any. This could be because the current sample contains no files from the current users (plausible, I haven't uploaded many files in Bugzilla) or it could be because files are not being attributed by their authors as of yet.
My understanding of this is that you can't get a list of uploads for yourself from BZ, the best it offers is a list of issues. This would be roughly equivalent to the subscribed issues list for users.
The context issue is:
Then obviously the author gets set via metadata to the actual user if they ever join. It seems equivalent to me?
Correct. Still you get a list of bug reports as the result for your query, not a list of attachments. And that should roughly equal in tasks that you are interested in anyway (and CC'ed on or commented on).