I re-read the same book about a year ago...
after several years of Christian worldview studies,
it made infinitely more sense this time, though it was incredibly insightful the first time.
Sowell has never come out and stated his faith,
but no one can have that great a grasp on the TRUTH
without biblical grounding.
The funny thing is, I thought over the years since I first read it that Sowell had used religious references in defining the constrained vision. Now I see that I superimposed my own religious faith on his language. But I think you are right that his philosophy and its source is there to see for those with eyes to see.