Nope, they were planning on staying in the airport for the night. Not that great an idea to be honest!!
Well I am pretty sure they would not have been allowed to remain airside and would have had to "Land" themselves so to speak through the domestic arrivals channel in T5. The Flight Connections centre would not have allowed them access if their onward boarding passes are issued to them. The last flight departs T5 at around 11pm and its pretty much lock down from then until about 4am the next morning!