Yes, that's what he was arguing, and the "why?" is precisely because
it demonstrates reactions like yours, and shows how emotional reactions
can cloud our minds. Questioning the motives of the proponent is a
classic fallacy of reason, as is following "common knowledge". I don't
happen to know whether or not gas chambers were used at Auschwitz--I
don't think it matters. Given the scale of the other atrocities, I
think that it's a minor point. What's the difference morally between
a gas chamber and a crematorium? But I think it is interesting to see
how attached some people are to that point, and how rigorously they
defend it with non-reason. Perhaps a rational treatment of that
question, as proposed, would indeed be a valuable document on reason.