I've kept quite a number of species on sand, including corns. I always fed in a bag or plastic container so sand impaction was never an issue.

A snake that is healthy to begin with is NEVER going to ingest sand. Why would it eat sand?

If it was very humid it is possible that the dust that is in the sand clogged its nostrils but then you would have seen it breathing through its open mouth.

As far as burrowing, unless it was mentally deficient, it has the instincts not to go deeper than it can burrow out of so I'd rule that out as well.

Incandescent lighting is fine for heat provided you do not overdue the wattage. A 50 watt bulb in a 10 gal. tank can give you a hot spot over 115 F. Too hot.

It is most probable that the snake was ill when purchased.

As far as the walking on sand thing, and not to bust your chops Joe, as bipeds we put all of our weight on a very small amount of surface area, the bottom of our feet, with every step. If you're like me that's a whole lot on not very much. A snake, having no feet, spreads its weight out over not only a larger surface area but has that larger surface area supported by the skeletal and muscular structure of a creature designed for being belly down on the ground.

Check the temps and see if they've had any other deaths at the shop.