Well, I'm not an expert in fine-grained materials, but let's try anyway:

The surface texture of the soil is a fine-grained texture with quite varied grain size up to about 0.2mm. It looks like clumps of even finer particles (1/100 this size or finer) forming the large "grains"

Grain Size Classification of Sediments:

Classification Grain size Wentworth size class
Gravel >256 mm boulder
32-256 mm cobble
4-32 mm pebble
2-4 mm granule
Sand 1-2 mm very coarse sand
0.5-1 mm coarse sand
0.25-0.5 mm medium sand
0.125-0.25 mm fine sand
0.0625-0.125 mm very fine sand
Mud (silt) 0.031-0.0625 mm coarse silt
0.0156-0.031 mm medium silt
0.0078-0.0156 mm fine silt
0.0039-0.0078 mm very fine silt
Mud (clay) <0.0039 mm clay

So that makes the aggregates of "very fine sand" size, although if you sieved it, they would break down and pass through finer mesh. The basic material is "medium silt" size or smaller. neither of these names should be used to imply anything about the materials. They could be "sand" (mineral grains and rock fragments), even if they are silt sized, or they might not be "sand" or "silt" at all, as we define them on Earth.

Remember the legend that Esquimaux have 200 diffetrent words for snow? I recall an SF book that began in this vein on Mars with dozens of different words for types of drifted fine material that were not sand or dust, but something else. So far we don't even have the words!

The material packs well under load, presumably collapsing those intergranular voids and forming a "welded" composite of equivalent density to the grains. (There could also be compression of the grains themselves - we need to see some pictures inside a tyre track, or where a rock has been rolled)

Analogies to cocoa powder or other cooking materials are good, in terms of appearance, but not in terms of behaviour. Although things like cornflour and cocoa do pack down into cohesive layers, they are very weak and not flexible at all.

The "fluffy" surface texture reminds me of fine grained, slightly damp beach sand, but much finer. By this, I don't mean that I think it contains water, but that something is sticking it together by suface tension or van der vaals forces in the same way that a trace of water helps sand grains stick together.

In summary, I don't think it's "mud" as we know it (clay minerals plus water). I don't think we have concepts or words for what it is - "Magic Carpet" will do for now!