posts are replicated to other systems via a broadcast-like subscription mechanism. each receiving system stores their own copies of content. as long as the remote system received the post and did not receive a 'delete' command, it would be available.
Yes, it also seems that the "delete" do not federated that well, and may come late.
However, on proprietary social media, d deleted posts are just "hidden", and there is various way to see deleted, moderated posts.
Despite laws like"right to be forgotten" and GDPR, assume that once you posted something on Internet it'll be there forever. Not a big deal if it's a graduation picture, or your time at last week end Marathon. More annoying if it's nude or a rant about "lazy immigrants stealing our jobs to get welfare"