Edit: obligatory explanation (thanks mods for squaring me away)…
What you see via the UI isn’t “all that exists”. Unlike Reddit, where everything is a black box, there are a lot more eyeballs who can see “under the hood”. Any instance admin, proper or rogue, gets a ton of information that users won’t normally see. The attached example demonstrates that while users will only see upvote/downvote tallies, admins can see who actually performed those actions.
Edit: To clarify, not just YOUR instance admin gets this info. This is ANY instance admin across the Fediverse.
Well of course. The instance stores all data in a postgres database. How else will it be able to remember anything?
Maybe this is not obvious to non-programmers but you never see everything in the user interface for any system. There are tons of records needed for the system to track everything that goes on.
Since posts are federated, they will exist in the local db as well as on each instance.