I think he is on the right track, but he is over-reaching by asserting Texas sovereignty over all powers not granted to the federal government by the US Constitution.

The 10th Amendment states "The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people."

His claim of Texas sovereignty over powers fails to exclude any claim by Texas over the many powers rightfully belonging to the people.