When I walked in 2014, I was wearing a distance tracker that send me an email at the end of the Camino to the effect of, "Congratulations, you have just walked the distance of NYC to Miami". And I thought, "Silly Jawbone!"
If anyone out there is wearing a satellite distance tracker (like a GPS smart watch), I'd be curious to know what the data reads are.
But it is true: how much you wander to see sites that are off the path, whether you take the main route or an alternate (like from Leon to Villadonga, and Orbigo to Astorga; the Oviedo from Pontferrada, the Valcarlos or the Napoleon start, the river or the industrial route into Burgos... these things will alter your distance from those of fellow pilgrims).
I bussed a total of 26k K on Camino because of illness and injury on the last trip, but I do not doubt that I crossed North/central Spain on foot.