In the scene where they finally approach the water hole, if you look at the prisoner's left hand you can see that the shackles aren't fastened at all. It falls so far down the back of his hand he could have easily slipped it off.
The sheep herder Changra is described as having been brought from Australia with the Tyson family. Australia is the only continent where the entire indigenous population maintained a single kind of adaptation-hunting and gathering-into modern times. More than 200 different Aboriginal languages were spoken and most Aborigines were bilingual or multilingual.
When the man at the depot loads his shotgun, you can clearly see the tan marks for a modern watch on his wrist.
Matt (tossing the shackles at the prisoner): Put those on.
Lorca (looking at the marshal in disbelief): These are for animals.
Matt: (leveling his gun at the prisoner): That's right. Put 'em on.
Quote heard on Album: "We've got about an hour of daylight left..." -Matt
This episode of "Gunsmoke" is feature in the album, Pink Floyd - "the Wall," but not in the movie version.