It seems an odd thing to have to apologise for...journalist v journalist wise especially. It was hardly libellous though something must have come into Newstalk on legal headed paper for him to say that
Or alternatively, he realised in the cold light of day that it made him look kind of stupid. Though if Hook apologised for everything he said that made him look stupid, it'd take up most of his show.
Can't see how it could possibly be seen as libellous, though. Just very unprofessional for anyone who calls themselves a journalist.