The Forbidden Spell 'Inverse Realm' is a powerful spell that can only be cast when five Demons with at least Arch Demon persona chants in unison. A powerful spell that could invert the laws of time, space, and force in any realm. This can only be done in a physical realm, but Adrian can guess that Olympus is not an ordinary divine realm.
Divine realms that have a god king living in them are actually rooted in the mortal realm. They are different because god kings are powerful gods that rule other gods. They are blessed to have some autonomy on the mortal realm where they anchor their divine realm. The God of Death Hades has experienced this once as Olympus has been subjected to this spell once when the Goddess of Life Gaea was angered.