The song is made of two parts which do not have any relation whatsoever:
Part 1 - In the 19th century, an anonymous popular song circulates with the words "guarija guantanamera," which means peasant-woman from Guantanamo. It was collected and arranged in 1932 by Joseito Fernandez, who made it the hallmark of his orchestra and popularized it as a dance called "Guajira-son," which he used in place of "Bolero" in closing every ball. "La Guajira" is therefore the name of a dance too.
Part 2 - It's not before 1958 that Julian Orbon combined this popular refrain with some quatrains taken at random from the immense poem Versos Sencillos
(simple verses) by Jose Marti. It commences with, "Yo soy un ombre sincero," but you have to wait for hundreds of verses before finding: "Con los pobres de la tierra." At last words well in line with the acclaimed Seeger -Guthrie protest song style. Marti never mentioned any Guajira from Guantanamo in those verses. As in many popular songs, you can't find any logical link between the verses and the refrain.