Ah, that would be an improvement: just re-read the article and I can't find any reference to "active use" vs "calendar". Can you point out where that is?
"seven days of Safari use without user interaction on the site"
It's not immediately obvious the way it's phrased but they couldn't be calendar days if there are days you don't use Safari; it's only counting a day as one where Safari is used and you don't visit the site.