About the Activity summary card
The Activity summary card appears once a month. It provides a very rough approximation of how far you've walked or cycled during that month compared to the previous one. These estimates are based on occasional samples of the accelerometer in your device, which are then compared to typical movements involved in walking or cycling.
This information isn't available unless you've turned on Location Reporting and Location History for at least one of your Android devices. If you've turned these on for more than one device, the Activity summary card reflects the one you used most often that month.