It is factually incorrect in stating that nitrite is not as bad. Both ammonia and nitrite kill fish in relatively low amounts. As stated above, it has been shown that nitrite is the worst to be succepted to at low levels for a long time, but both are deadly so you don't want either.
Also, somewhere around 80% of the ammonia in the tank is from osmotic reactions across the fishes's gills, so referring to the ammonia as being converted from fish-waste doesn't give the correct status.
However, as a simple step guide it does show a lot of promise.