Thank you so much for your informative and timely response!
My information comes from estate papers of Mastin Anderson suposedly on file in Tarrant Co., Tx. There is a petition for adminsitration on the estate of Mastin Anderson and it states, "late of said Tarrant who departed this life while in the Army of the Confederate States in the county of Smity, Texas." The petition was filed Sept. 1, 1862. Therefore, you may very well be correct in that he died of disease or other means. At this point, I don't know why he was in Texas in the first place but I do have record showing him as a resident of Tarrant Co. in 1860. I will try the link you gave for Smith County and again, thank you very much.