Pi is not a variable. I was very careful with my wording to say things like "variable", "expect to change", and "mutable state" so my statement would apply generally. :)
Your wording might have been careful but the author did use pi as a variable in his example and discussed wanting the ability to change it. Since you were essentially agreeing with her/his point, it's forgivable if one then assumes you were also agreeing with his example as well. Hence my counterexample (and hence why I opened with "Generally yes" to signify that I don't disagree with your point but the example provided needs tweaking)
I'm not sure I was agreeing with his point, since I only consider one of his configurations 'valid', and even then only insofar as Pi is a variable (which it isn't). My original statement holds generally and specifically--pass in the things you may want to vary; don't depend on global mutable state.