Hi
To credit progress towards your daily 30 minutes Exercise goal, the Activity app aims to identify activity that equals or exceeds the intensity of "a brisk walk".
It is possible that only parts of your walk met this requirement.
The definition of a brisk walk varies from person to person and depends upon your personal information.
To check that your personal information is accurate - and to update it over time:
- On your iPhone, in the Watch app, go to: My Watch tab > Health > Edit - tap and adjust items, then tap on Done.
During general daily wear and during workouts when GPS data from the paired iPhone is not available, the Activity app relies on your arm motion (measured by the accelerometer) to track movement for the purpose of crediting progress towards the Exercise goal. For the best results, allow the arm on which you are wearing your watch to swing naturally as you move around.
Calibrating your watch also helps to improve the accuracy of various estimations (including Exercise credit) made by the Activity app and Workout app. More information and instructions for calibrating your watch are available via the link below.
More information:
Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support
Use the Activity app on your Apple Watch - Apple Support
Use the Workout app on your Apple Watch - Apple Support