we're (essentially) talking about revealing somebody else's hole cards after the hand is over. Indirectly, yes.
I kindof agree with Lukie on this one. Maybe not unethical, but maybe bush league (ie: unprofessional/cheap). The kind of action that the other players in the room would look at and think "Wow, what a dick".

And I also agree that he should keep that info to himself (if he was indeed holding the A) and use it against both players later in the tournament.