Where in the docs did you come across this?
The inconsistency was found in Chapter 4.4 "Implementing Life".

Describe what about it does not make sense
For most of the chapter the American English spelling of "neighbor" is referenced, however a few of the code comments use the Non-American spelling of "neighbour".

Why does it not make sense?
This is by no means a significant issue, just thought it might be useful in cleaning up the wonderful book further.

How could we improve it?
Since the American English spelling is predominantly used, replace all occurrences of the "neighbour" spelling with "neighbor".