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.
That is because of how ActivityPub works. Action is pushed to alle instances that subscribe to the community. Posts, upvotes, downvotes, comments, everything is also stored on all federated instances. There is no way to make absolutely sure that all servers delete your data.