The prophecy did NOT come from legends, it has been written form the start of time.. It said that one woul come and bring balance to hte force, no body actually said it was a Jedi prophecy. Obi-Wan himself says this in hte book of Ep 3, he says 'Exactly, but nothing says he has to be a Jedi..' to padme in their apartment (A + P). So for all we know, hte prophecy could have been picked up by hte wrong folks