[The Aussie hostage survivor drank the bar dry and sang Waltzing Matilda...]
I first heard that song at a Tommy Emmanuel concert. He said the tune is an old Scottish one but the lyrics are Australian.
The lyrics are definitely Australian - written by Andrew Barton 'Banjo' Patterson, one of Australia's greatest poets.
The tune is much more complicated. Originally, the song was played to a tune composed by Christina MacPherson in 1895. MacPherson said that she based it on a tune that she had heard before - Thou Bonnie Wood o' Criagielea which is a Scots tune. The thing is, there's actually not that much similarity at all between Criagielea and the original Waltzing Matilda score.
Regardless of that, though, the version that is most commonly played today is legally accepted to have been composed by Mary Cowan sometime before 1903 (the words were also slightly changed at that time, according to legend in order to advertise "Billy Tea").
This tune is also used for a British song, The Gay Fusileer but it's unclear which came first.