Rio along with Amelia and Artemis came out of the teleportation gate. The entry to the islands was only accessible through space magic, as the normal ways of traveling couldn't work. Flying was prohibited around the floating islands and walking or vehicles were impossible to come.
Airships, which are often used for air travel or flying treasures which are used for flying in the sky, aren't allowed to enter the vicinity of Laurelia Sanctum. There's a barrier surrounding the island and the only way to pass through that is either with the tokens issued by the world association or with the permission from the principal of Zenith academy. Forced entry or unauthorized stay in the airspace would be dealt devastation and no questions or explanations would be asked.
Since the ceremony had already started, all the guests were already present inside, so other than the guards and security staff stationed at the gate, no one else was present.