There's a difference between aerobic and anaerobic exercise. For many people, that manifests as walking being different from running. Which "zone" your heart rate is in (as compared to your maximum heart rate for your age group) tends to be a good indicator of which kind of exercise you're doing. It's important to do both kinds of exercise, with an 80/20 rule being pretty commonly followed.
The 80/20 rule is kind of bullshit unless you're a professional endurance athlete. People who are only exercising a few hours per week will probably benefit from spending more than 20% of that time in higher intensity zones.
