I was surprised too. In the article you posted he says Trump isnt a good candidate. Here is another.
http://m.townhall.com/columnists/thomassowell/2015/08/04/the-trump-card-n2034124/page/full
I am hoping Sowell is turning but your link indicates that might be a pipe dream.
Why is that a surprise? Sowell has never endorsed socialism or liberalism in his career.