As l understood it, at least until recently, it was impossible to run a train on the East Coastway, and then connect straight onto the line up to London, without a very complicated manouvre just outside Brighton station that involved reversing the train onto one of the platforms and then out...
Maybe they knew something that we didn't and were simply encouraging us not to travel. If only we had taken the hint and gone home, we might have had a far more enjoyable evening. :)