My theory. There are two Skiddo that were apparently abandoned by their trainer outside of the train station. In the train station is that suspicious note that says 'meet me in the usual place'. Some people theorise that the girl in the hotel is the ghost girl. There is also a woman who comments on losing her lover in Lumiose before battling you and giving you a destiny knot.
A businessman from Lumiose was cheating on his lover (the woman who gives you the destiny knot) with a hex manic from outside of town. The hex manic would regularly get a train to Lumiose and meet up in his office while he was working (the second floor of the building where you meet the ghost girl). The hex manic would also stay in the hotel while she was there. The man owned the two Skiddo. On one such meeting, the man's lover began getting suspicious and to hide the truth, the man staged an elevator accident to kill the hex manic. The man panicked and left the city, leaving his two Skiddo there for unknown reasons (perhaps he caught them as a symbol of love to the original woman now feeling due to being dishonest they didn't symbolise anything). Now the hex manic ever patiently waits for him to return to Lumiose and come back to his office, staying in her hotel room while the man's lover suffers from a broken heart.
In any continuation of the game, it is my theory that you will meet this man and take him back to Lumiose to face up to the issue. It seems to make sense to me but it's just a theory.
