Yes, Flip. In the time before processed foods, people foraged for food and that would be what a Rasta would eat (as you said, minus the meat) and then later an agrarian culture grew cereal grains and fruits and vegetables. Again, what a Rasta would eat.
Much of the Rasta's diet comes from selected scripture verses that Marcus Garvey used as a basis for the Rastafarian lifestyle. Here is some information about the movement and Marcus Garvey. http://www.jah.com/rastafari-movement/
A true Rastafarian is about discipline in his way of living. The way he eats. The way he is true to his word etc. I am afraid that many of the dreadlocked people you see in Negril use the look as a camouflage to get close to people. Who dem cap fit, let them wear it.
Peace and Guidance