Just checked the Aer Lingus website and can see that it is re-advertised alright. Very odd. The only thing I can think, is that presumably the situation changed after the interviews closed. Eg. EI were initially approved for 2 cadet schemes, but then they got approval for a third scheme so in essence the goalposts have changed.
What is there to stop somebody who reached interview stage back in Sept. applying again and doing really well as they had recent exposure to the interview process? We may wait and see!