Half-wave rectifier with diode connected nMOS and pMOS
Q1: In this circuit the transistor is sometimes reversed, i.e. source becomes drain and vice versa. Still, I would say it is a mistake. The circuit however looks OK.

Q2: This question is already answered in the text. The PMOS does not suffer from a threshold increase due to body effect. Moreover, the terminal with the arrow ("source") is P+ and the well connected to the other terminal is N doped, so you get a body diode for free, which helps as well.