Myth-making seems to be an important part of the folk process. I can see how someone might draw a parallel between Tubman, and her escorting of slaves to freedom, and the biblical Moses, but "Go Down Moses," the song obtained from the Contrabandists, is certainly just a religious song.
Several songs have been suggested as having significance to escaping slaves. A few, such as the one quoted from Bradford, could have been used as pre-arranged messages in the area covered by Tubman, but for others often cited as directional songs, e. g. "The Drinking Gourd," there is little evidence of such a meaning. The inferences were drawn many years after slavery by the myth-makers.