I have no idea what 'sedentary' even means. I work on a desk mostly but I also walk 15 - 20 k steps per day because that's just my life and I accomplish most daily tasks (shopping, going to park, coffee, etc walking). Is that sedentary?

According to the study:

  Sedentary (SED, n = 9): No regular exercise or elevated heart rate beyond daily tasks. Active (AC, n = 10): ≥150 min/week aerobic exercise for ≥6 months.