Out-Degree of a Configuration Graph
Based on some research into other things related to TMs, I discovered that any NDTM that has at most $k$ possible branches at each step can be modified into an NDTM that has at most $2$ possible branches at each step at the cost of a $\log_2(k)$ slowdown. Though I can not find any mention of this anywhere in the textbook, I assume this is what the authors are assuming.