That might be true for jody calls in the military, but jody calls go all the way back to 17th and 18th centuries when work crews and slaves sang what is called "call and response". Where one person would sing a line, and the rest of the crew would repeat the line. Just like military cadence. Jody calls from the old days would be used to pass time and/or keep pace while working, or in churches in rural areas where much of the population couldn't read the hymn books.