More likely it was La Bamba that was the 1st folk/rock song because I heard it's indeed an old Mexican folk song.

The oldest folk song itself is The Song of Solomon (sah-lo-man) in the bible.

Then there's a very old instumental song that I can't recall the title of but it dates back to the days just before the dark ages.

I recall reading that the oldest song period is,"The Shaduf Chant". Never have heard it.

As for folk rock,oyu just might be right! ;)

La Bamba is indeed an old Mexican folk song; if anybody ever goes to Mexico City and sees the Ballet Folklorico, or if the Ballet comes to your city, you can see/hear a more traditional version of it--it's a wedding song, and it's lots of fun both aurally and visually.
DQ