We can clear that one up rather quickly. If you have an opportunity to review his service file in Capt. R. T. English's Company, Mississippi Light Artillery, he is listed on roll as a private. However, he is listed among Confederate medical officers in the garrison of Port Hudson LA, July 10, 1863. His rank is given as acting
Assistant Surgeon. Given the dire circumstances at that time, Hornsby must have been need to care for Confederate sick and wounded, and was referred to by a temporary rank. He was not a commissioned officer.
You may wish to check O. W. Hornsby, Co. "E", 4th Louisiana Battalion.