The suit does appear to be sandtrooper .
We all know the sandtroopers were filmed first in tunisia, then cleaned up and modified for use as stormtrooping in England.
Maybe unmodified sandtroopers were used for shots when the troopers backs are turned ? Maybe a time saver ?
The belt/holster has already been i.d.`d from screenshots (pictured from behind only) The holster is a slightly differant shape to all the others seen on screen , maybe the first one made ? The term prototype sound so nice ...
Whatever the story , the fact that it is a sandtrooper and that the helmet is such a sharp pull indicates its an early suit .
The utility section of the canvas belt is indeed the same plastic as the rest of the suit.