The flight will have been late because it was the aircraft operating the Amsterdam flight in the morning. Holland is very susceptible to fog at this time of year; in fact this morning's flight also had a fog delay.
I'm not sure what will have caused the handling problem. At a guess, an hour's delay on the Rome flight will have brought it in at almost the exact same time as the Malaga and Heathrow flights. I doubt there are enough Aer Lingus ground handlers around at that hour of the evening to deal with three simultaneous arrivals. It could also be something stupid like all the available steps having been attached to the other two aircraft because nobody considered that the Rome flight was running late.
Talking of which, what is the current status with the airbridge? The cones have disappeared from the bottom of it. Is it back in service?