Christ. Ben Smedstad was still a producer during BG2's development, he could just as easily have heard the story from him.
That doesn't matter whom David heard this from, either James or David is wrong. Can't both be right. Human or githzerai? Whom do you believe and why?
Not to mention that Ben would've likely corrected people if they were wrong about Xan's original class.
Clearly didn't correct them about "Xan's" original race, so that's unlikely.
Instead of addressing any of my points you just enter fantasy-land where everything is possible. Everything except the painfully obvious.