Under what theory? The troops were State troops, mustered by the State and furloughed by the State, no officer objecting to their going home. The Union had no authority over them, pretended or legal, theoretical or pracitical. The Union forces at Brownsville had just had their asses handed to them, and any serious Union effort was weeks, months away at the earliest. Both the Army of the Potomac and the Army of the Cumberland were in the Washington area and ready to go home themselves. Tell me another.
The confederacy started losing the war almost from the first day, was at no time ever close to defeating the Union, and it just took 4 years for the corpse to hit the floor.
In your own mind, Yank. You've got to stop believing your own propaganda, it'll rot your brain.
On the other hand........go on believing it. Don't let me stop you.
Now you're just being silly. The rebel troops that surrendered at Appomattox with Lee and in North Carolina with Johnston and yes, in Texas were parolled by the federal authorities after their commanding officers had surrendered. They lost, they were whipped. Deal with it.
In your own mind, Yank. You've got to stop believing your own propaganda, it'll rot your brain.
I realize that the truth is unplesant to you but that can't be helped.