Thanks for you post. I read Jay's statement almost the same way you did. After reading it again a time or two, I see that the statement is "most of the Confederate soldiers from Texas" belonged to the KGC. That's an even bolder statement than we thought it was.

Evidently Frazier's book (which I have not read) makes this claim, or something along those lines. This link includs a partial list of publications concerning the KGC.
http://www.nationmaster.com/encyclopedia/Knights-of-the-Golden-Circle