Translation:One can have a particle of snow, sand, bread, and many other things.
I think it's because you are not talking about the amount of snow or sand ("one particle of snow" as an amount) but merely about the fact that the particles can come from there ("a particle of/from snow" as origin or material).
A bit like the difference between "glaso da vino" (a glass of wine = quantity = glassful of wine - tells you how much wine you have) versus "glaso de vino" (a wine glass = tells you what kind of glass it is, i.e. one suitable for wine because of its shape).
So an "ero de neĝo" tells you what kind of particle it is rather than telling you how much snow you have.
If you said, "Oni povas have eron da neĝo, sablo, kaj pano" I think it would be "You can have a particle's worth of snow, sand, and bread".