A mushroom with a body and legs? Also, I don't recall hearing of any ritualistic use of mushrooms by the Egyptians; seeing as how they made nice paintings depicting all sorts of rituals and wrote up detailed recipes, this seems strange. Can you point to any texts which detail mushroom use?
People from further East, had penetrated this wild zone and were "dong their thing".
The "mushroom" was a natural object. There was no body or legs at the time. That awaited the time far in the future when the Egyptians would dig down into the sand, cut block and b build pyramids.
They simply left the mushroom intact until they cut the face into it.
It's kind of like how the Moslems took over Saint Sophia. They left the building but added minarets.