Tangledwood, apparently it was an Australian TV game show in 2007 that got Larrikin's attention. I quote from http://www.news.com.au/entertainment/music/quiz-show-sparks-aussie-anthems-battle/story-e6frfn09-1111117725552

Mr Lurie [Larrikin Music Publishing managing director] said the alleged Kookaburra connection was raised on the ABC TV show.

"This question was posed on Spicks And Specks: 'What children's song is contained in the song Down Under?' The answer was: 'Kookaburra'," Mr Lurie said.

"The next day, my email and phone lit up with people asking: 'Do you know about this?'