If he'd fallen down in snow. It would have melted not leaving any dirt but a wet spot or be white.
If he had fallen on dry dirt is would have just brushed off, like the ashes from my wood stove.
It had been snowing and was still very cold during that week. The ground was frozen. Falling on it would be like falling on rocks. It would not adhere to his clothes.
What appears on his clothes is mud. He was knocked down in the mud....
Where was there mud?
Construction site