Earth architecture

Reading a book by Peter Frey,  Learning from Vernacular: Towards a New Vernacular Architecture,  I came across the phrase:
"Earth architecture represents a way of ecological construction that requires only 1% of the energy that is necessary to erect an equivalent building made of concrete or bricks,  and returning it to its original state requires no energy at all."
When I looked into constructing an earth (one of the options was cob) building as a vegetable storehouse,  I ran into problems with designing foundations.  So the first miscomprehension with the above sentence would be believing that the *entire* building can reduce energy so dramatically.  Typically there is some stone,  brick or concrete construction required too. Secondly,  are we not calculating human labour involved? Because gathering the earth required is laborious -  it should be subsoil with less organic matter than topsoil so deeper digging required! Return to its original state... don't mistake this as implying that the building will leave no mark or footprint when gone- remember those foundations?  And the roofing will likely not be earthen either.