At low temperatures, ice is just another mineral.
2% (I presume that's by mass) is a lot of moisture for an arid climate soil.
Some of that is in the form of water ice, permafrost. But I wonder how much is locked up chemically in the rocks, or as a hydrate or in solid solution with something else. That would be less likely to sublimate in warmer temperatures and eventually be broken down into oxygen (which would go right into the rocks) and hydrogen, which would escape into space.
The text mentions the soil is toxic to microbial life. Would it be toxic to humans if they brought some into a spacecraft, say, on their boots?
It must be a very strange place.