Thanks for your information. As I said I was "pretty sure" which isn't to say "sure" or positive and possibly incorrect. I do see see what you're referring to. My understanding on how activitypub works to federate is that it's sent FROM lemmy.world and the originating user TO slpnk.net as it lists in the heading just like sending email from one server to another. The Lemmy Devs mention this at https://join-lemmy.org/docs/introduction.html "Just like a traditional website, people sign up on it, post messages, upload pictures and talk to each other. Unlike a traditional website, Lemmy instances can interoperate, letting their users communicate with each other; just like you can send an email from your Gmail account to someone from Outlook, Fastmail, Proton Mail, or any other email provider, as long as you know their email address, you can mention or message anyone on any website using their address."

From my understanding, Activitypub uses lots of copies just like there is a copy of this post on any Mastodon or other Fediverse servers that are federated with us so there may be more than one server hosting the image. If you click through on the link above you may find some useful explainers and you might get a more technical response from another Fediverse focused community like fediverse@lemmy.ml or activitypub@lemmy.ml