As far as I've read there was never a confirmation by TPTB - that doesn't mean anything, I know, it could have gone past me.
The same for source books - there was never a confirmation, hard evidence, only assumptions. It fit so damn good, and the people fell in love with it.
But evidence? No. Just a theory, nothing more. A theory proven wrong by this one sentence in J:FR.
It's possible you're correct and the writer made a mistake. But so what?
Personally I don't care who the Master was. He's dead, Jim.