I cannot readily speak to why you are not seeing sequence ownership as a dependent when looking at the now-archive table definition.
pgadmin knows it's a dependency because when you try to drop it you get a message saying so but I can't see it in the defintion of the table.
BTW is there a way to get a list of dependencies for a object? I was some scripts when I was googling but none of them seem to work with later versions of postgres.