Neat photo and a very cool carved holster!
It doesn't look like the holster had been in that spot very long. It's positioned right over a bunch of cartridges in loops and there's a lot of space between the top of the gun belt and the inside top of the holster loop. I'd expect it to conform to the belt and loops after extended use and cause the belt to sag on that side. The top of the belt looks straight as an arrow!
I suspect he normally wore the holster on his right side and repositioned it at the photographers request, so it would be visible in the picture. "Artistic license"…
That would also explain the look of contempt on Unibrow's face!
"Darn fool Easterner…. Only a dang greenhorn would wear his gun like that!"