Actually, King loved the new ending: http://www.firstshowing.net/2007/stephen-king-approves-of-the-mists-new-ending/
I think King has become more of a dour, crotchety, bitter, a-hole as he has gotten older. I think that helped him like the nihilistic and hopeless new ending - because it’s just like his outlook these days.
If the King quote I heard/read was accurate, it certainly came across to me as sarcasm. Your mileage may vary, of course.