Following my previous question (with great answer from Bart van Ingen Schenau), I noticed a discrepancy I could not wrap my head around:

Bart mentioned that:

The point ON the boundary is by
definition the closest you can get. For a closed domain, this point is
defined to be the last point inside the domain and for an open domain
this point is defined to be the first point that lies outside the
domain.

It perfectly works when applying for integers or real numbers but I found a following article in an book. Note the increment is 0.5.

But I still do not understand – when Size > 4, they consider 4.5 an ON point but it does not fit the definition – “first point that lies outside the domain.” because 4.5 is IMHO in the domain as it is greater than 4. Not sure what is actually the first point outside the domain if 0.5 is the increment..
What is the catch here?