I've heard of the whole Mandalorian race thing before (from the Marvel comics, I believe?), and I also remember all the early speculation that Attack Of The Clones would feature a battle between Jedi and Mandalorians that would arrive from jump ships someplace called "Concord Dawn." But its all hooey. The source I rely on is a mention made in one of the novels (I can't to be honest remember which one at the moment, but I'm wanting to say it was "Tales of the Bounty Hunters"), which is newer and which Lucas has at least given the status of canon-until-I-specifically-say-it-isn't.

And that says it is a
material.