Ha! ha!
I've just seen this. Maybe they just got bored waiting
The abrupt ending anyway made no sense in a pre-recorded show- X Factor always ended a bit 'is that it'- after 4 months of build up, the winning act would be showered with confetti, mobbed by the 'losers' and try and sing as the credits rolled.
There really was no excuse to end this so swiftly- even if there was a bit of technical issue or 'Adele' couldn't compose herself to sing again-- they could have re-done it, and we wouldn't have been any the wiser!