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.
No, Lemmy currently doesn’t do authorized fetch and thus there’s no way for users to request access to a certain post, which would sort of require to disclose a user wanting to get access to something. So no, they are not stored as part of activitypub.
They could be logged on your instance’s server and/or the server where are an image is hosted as part of typical logs for web requests. These would contain your ip address and other browser metadata such as the user Agent, but these are typical logs that happen every time you load anything on the internet on any website that exists.
Thanks