Of course a river's course moves back and forth but it is still the border of Texas. What do they think that it is now Oklahoma? We have a friend who is now retired but he was a ranch manager for a family owned ranch even bigger than this one. He now lives in Wichita Falls. The ranches were in the Texas panhandle and north central Texas. I'll bet he knows all about this.
You can bet your friend knows all about it.
Short but informative Farm Bureau-narrated video about the case:
http://www.youtube.com/watch?v=4sAbiO0SThQ
My family has ranched in a county bordering the Red River for almost 150 years. I do not know the individuals involved in this case, but am in total agreement with them.