What the author bases this on is not traditional Feng Shui. Traditional Feng Shui, stripping away the mystical and superstition does not use or worry about mirrors.

Much of this misunderstanding comes from a Chinese classic referred to as the 8 House Mirror theory. It discusses how if you know the 8 house methods well, you can see what is happening in the house as clearly as if looking into a mirror. Much of early Feng Shui knowledge was passed down as poems and often these analogies were used to confuse people to keep the real method from being disclosed.

We recommend that you read our Article on Mirrors posted here.