Of course, as Colonel Simpson said, Hood was writing after the war, his tenure as commander of the brigade was relatively brief, and his book is replete with mistakes. I seriously doubt that the men who served in the brigade througout the war, unlike Hood himself, would have forgotten something like origin of the sobriquet "3rd Texas". I know from my own experience that memory can be faulty. :-)
Nothing in this exchange should be construed as a knock on the 18th Georgia. Likewise, the 18th Georgia doesn't need any embellishments or "good stories" to enhance its already sterling reputation. The 18th Georgia was one of the finest regiments in Lee's army of heroes.