That's a very different recipe from the one that mine is based on, which seems have been moved to this URL: Texas Chocolate Sheet Cake
The batter is much thicker and the frosting uses regular sugar and milk rather than powdered sugar and buttermilk. Not gelatinizing the flour by pouring the hot butter/cocoa/water on it would change the texture a lot, too.
If you search for Texas Chocolate Sheet Cake, there are a number of different recipes. Some of them use Dr. Pepper in the batter, which would be a very Texas-like thing to do.