I would go for eccentric. It didn't seem to be a prank - he was friendly but quite earnest. I just took him for a free spirit sort of person.

The way he just launched into it so confidently made me think that maybe he does this all the time. Maybe he figured that the agent at the ticketing desk could easily pull up a list of all available seats leaving from Hong Kong that night and give him a list of possible destinations.

Frankly in this day and age I would think you'd need to be careful about that sort of request. Anyone who just wants to get on a flight without caring where it goes could easily be seen as suspect by security officials.