The took advantage of an oppurtunity to sell a unsold ticket by use of force to someone who already had a ticket, for circumstances that did not require him to purchase an additonal ticket.
In other words, they saw a fat guy, and decided to force him to buy another ticket, when they knew dang well, that they would have extra seats.
I maintain that a tired skinny guy who wants to stretch out and sleep has just as much right to the extra seat.