I usually don't answer unknown numbers but this was at least a Dublin landline number. Still, I am taking a caller's word that they are "AIB". I did have a transfer that had not been processed, so at least it seemed possible. Ironically, I failed their security checks! I couldn't match my address to what they had on their system. At that stage I was getting fed up and said I'd call back.
It seems that AIB and PTSB will directly call you whereas Revolut, N26 or Raisin will conduct all interaction via the app.
When I did phone them back (and satisfy the security checks), they then gave me a series of warnings about scams - I pointed out that a cold call from them wasn't especially reassuring earlier. There does not seem to be a common standard as to how legitimate contacts are initiated.