If you stop to think - The Arann would have been using single engine taxi (to reduce fuel consumption, etc (the ATR was designed to be operated in this mannor) - given that the adverage taxi time in DUB is between 30-40 mins on an adverage day. And as for the engineer under the wing they could have been carrying out a line check or any mannor of regular or routine checks.
Rumours like this do not really help anyone - although I do see and understand that you were just asking or wondering