I have noticed that with Americans - saying tune when they mean song; and sometimes song when they mean tune.

There are probably some places where some kind of instrumental accompaniment for singing is traditional. Flamenco, and North African Music I believe. But not in the British Isles, or indeed in most of Europe.

Alongside this there is the more courtly and formally composed types of music and song, such as Carolan, or Elizabethan Lute accompanied songs, such as John Dowland.

Musical accompaniment for folk songs and for songs in a similar idiom is a relatively new development, a new tradition.