All I can say that particular passenger is probably ignorant of how low cost airlines work. Most low cost airlines do not issue out assigned seat numbers. All you get is a boarding pass and you can choose where to sit, except the crew seats, of course. The reason being passengers will tend to be on time when there is no assigned seat.
If the passenger intends to sit in a particular seat (window, aisle, front, back, etc) or with fellow travelers, then the passenger should arrive early in the airport and be the first to queue up at the boarding gate. If a passenger arrives late, then the passenger will most likely have to sit somewhere they do not want like the passengers I mentioned earlier. So, in order to avoid such a problem, always always arrive early at the airport. Otherwise, you’d be complaining like the passenger I met.