When was it ever considered that the desert might be "man-made", or otherwise anthropocenically-induced?
El-Baz has utilized satellite images to better understand the origin
  and evolution of desert landforms. He is credited with providing
  evidence that the desert is not man-made, but the result of major
  climatic variations.
  
  Does the passage refer to all deserts?


Geolmorphologists classify deserts as zones that take place in climatic arid regions where rainfall is relatively low, there are extreme daily temperature variations and the vegetable cover is reduced or non-existent. The climatic conditions result in desert typical forms as hamadas, caliches, or dunes. (Gutiérrez Elorza, M., 2008).

It is important to note not every arid region is a desert, but every desert, with particular forms, is an arid (or hyperarid) zone.



Source: research.net

The question is: can Climate Change and deforestation create deserts?

Answer is Climate Change and deforestation can create new arid zones. It can create the conditions to expand existant deserts, but the typical desert forms take some time to form, so deserts as El-Baz have not (yet) grow because of our actions on the planet.

However, other deserts as Sahara have expanded his area in the last century (Thomas, N. et al., 2017). The article of this asseveration quotes (anthropological) Climate Change as the main factor of this expansion. 

So answering your question the passage you quote does not refer to all deserts if you consider man-made something that result from our emissions of greenhouse gases to the atmosphere.



Gutiérrez Elorza, Mateo (2008): "Geomorfología", Ed. Prentice Hall.

Thomas, Natalie and Nigam, Sumant (2017): "Twentieth-Century Climate Change over Africa: Seasonal Hydroclimate Trends and Sahara Desert Expansion". Journal of Climate, vol 31.