Gus warned them on the plane that they would likely be there for quite a while. The politics of New Vista didn't carry across seas even if the Morelli fortune did. They would be left alone for a lot longer in a generally more peaceful place than the city they left behind.
Since Ethan didn't ride the elevator and his competitive nature had him rushing up the stairs to get there first, he was already settling in when he heard the door down the hallway close and Rachel had gotten to her room.
He was hyper-aware of her existence since the walls between them had broken. He gave into her teasing and let it linger in his thoughts for a long time.
To be polite, he had shut the bathroom door between the rooms when he first arrived in case that was the room she chose. When he heard her start putting her things in their shared bathroom, he decided to get even with her and scare her.
She hadn't locked the door so he went out on a limb.
