You've got me laughing! Yes, my weakness for finding complexity (or more likely inventing it) in the simple has done me in again! You are most welcome to use my weighty explanation anytime you want.
It was really the word that caught me -- it's modern. And yeah, of course I had to go and look up 'sidewalks' just now (uncontrollable habit unfortunately) and discovered that in the US at least the conventional "what we see in our heads when someone says 'sidewalk" began in roughly the 1860s in San Francisco. Yes, always for centuries walkways and pathways and byways etc.
Oh my. I am just quite happy I dragged this out of you in a small space rather than on a large stage somewhere. Hats off again to your honest and disarming reply.