No, it's not a question of their physical location for the break - whether on or off the aircraft. The question is about not being visible to (and therefore available to) passengers during their break. So on aircraft is fine, if there are no passengers on the aircraft at the time of the break.
They want a break where they are not going to be interrupted.
The union didn't agree to removal of an unterrupted break, or to operating on call.
Probably Morning Ireland interview, as I don't get to listen to anything else much at present, but honestly, I'm not 100% sure what interview I heard.