Question About Floating Point System
After reading further, I found the answer. The answer is that the $x$ given in the question is not in $\mathbb{R}(5, 3)$. The way I figured this out is as follows:

On the next page, the author states that 
$$\min_{x \in \mathbb{R}(t, s)} |x| = 2^{-2^s}$$
This is consistent with $(.100 \cdots 0) \cdot2^{-(11\cdots 1)}$ being the least positive number in $\mathbb{R}(t, s)$, and not $(.000 \cdots 01) \cdot2^{-(11\cdots 1)}.$