This makes sense if you consider the original meaning of the word:
* Old English "mold" referred to soil or earth.
* Later, it was used for "a soft, loose, and often damp earth", which is similar to the substrate where molds grow.
* Finally, it evolved to refer to the fungi themselves, which are often found in damp and earthy environments.
So, the word "mold" traces back to the concept of earth, highlighting the natural environment where these fungi thrive.