"I seem to remember the song “Waltzing Mathilda” from when I was a child - and that was way before 1980. Just sayin'"
LHG, And the Band Played Waltzing Matilda isn't the original song by Banjo Patterson which is, as you rightly pointed out, over a hundred years old. Although it was older than 1980; I remember it being played at a school assembly in at least 1979.
The above quoted song is about a bloke who goes off to the trenches* of WWI, gets his legs blown off and his reward is to be met, at his his arrival back in Sydney, by a band playing Waltzing Matilda. I assume that the song by Eric Bogle is meant to be a pacifist piece about the evils of war.
*Gallipoli, specifically