I don't have Razavi's book off hand, but my guess is that he was using a resistive load. Notice the words "may" and "For example".
For your first answer, the current is given by (Vin-Vgs)/R. In this case, he was stating the numbers from a hypothetical R load that will give the mentioned figures.
For the second answer, refer to the first one. If the body is not connected to the source, you will have another non-linearity due to the body effect. If it uses a current load, then the output impedance of this current load introduces yet another non-linearity.