It certainly looks as if the problems those travellers encountered were handled badly by all involved but I wonder if they were advised of the Andrews Taxis cab-share scheme. This offers those who have missed the last London train the option of a taxi at £20/person (subject to a minimum of £100 in total) in a 7-seater taxi. Being backpackers they may not have wanted to spend that sort of money perhaps.
The airport operating hours are actually shown on the LSA website in the 'Check In Preparation' section:
"Passengers should be aware that the terminal building is open between 04:00 and 00:00. All passengers arriving before 04:00 will not be allowed access to the terminal."
That information could certainly be more prominently displayed perhaps.