Funny thing is, your post isn't actually deleted in the database of the hosting fediverse server either. It's still there, and you can restore it.
Deleting your account "should" delete the database entries for your user account, and propagates a delete command out to the fediverse, but the fediverse can choose to ignore it as well.
It's all a bit odd.
That's an advantage - so you can contact them for a copy of your lost data if you ever need it. Helpful!