His logic is flimsy at best. Sure, being a French girl in the Middle ages didn't equal being white, but sure as hell give you a shit tone of possibilities of being one. Specially one born not in a city or a coastline where you could pull out the 'merchants from other places' excuse. She was born in what today is Lorrain, in the middle Europe for God's sake.
And there's also the fact we have so many recounts from other people about her, in a time people were openly racist and no one mentioned her skin colour, only her dark hair. Hell, the Englishmen were pushing stuff about about her being a heretic, wouldn't they have also brought up 'she is not white, ergo she is not even Christian' at some point?
I just can't with this people.