I did a google search and found nothing about "mountain" being non-PC. If anyone ever finds out what the author is talking about, please tell me.
Perhaps because it implies that the mountain never did come to Muhammed :)
"The Language Police" by Diane Ravitch talks about how grade school textbook publishers have "sensitivity panels" that do "bias reviews," removing references to things that might be offensive to any conceivable group. Stories set in hills and mountains have been omitted for being "regionally biased," and thus might harm the self-esteem of kids who live in the plains.